``ll.ul4c`` provides templating for XML/HTML as well as any other text-based format. A template defines placeholders for data output and basic logic (like loops and conditional blocks), that define how the final rendered output will look.

``ll.ul4c`` compiles a template to an internal format, which makes it possible to implement renderers for these templates in multiple programming languages.

Apart from this Python implementation there are implementations for Java (both a compiler and renderer) and Javascript (renderer only).


=========
Embedding
=========

In the template source any text surrounded by ``<?`` and ``?>`` is a "template tag". The first word inside the tag is the tag type. It defines what the tag does. For example ``<?print foo?>`` is a print tag (it prints the value of the variable ``foo``). A complete example template looks like this:

   <?if data?>
       <ul>
           <?for item in data?>
               <li><?print xmlescape(item)?></li>
           <?end for?>
       </ul>
   <?end if?>

(For text formats where the delimiters ``<?`` and ``?>`` collide with elements that are used often or where using these delimiters is inconvenient it's possible to specify a different delimiter pair when compiling the template.)

A complete Python program that compiles a template and renders it might look like this:

   from ll import ul4c

   code = '''
       <?if data?>
           <ul>
               <?for item in data?>
                   <li><?print item?></li>
               <?end for?>
           </ul>
       <?end if?>
   '''

   template = ul4c.Template(code)

   print(template.renders(data=["Python", "Java", "Javascript", "PHP"]))

The variables that should be available to the template code can be passed to the method ``Template.renders`` as keyword arguments. ``renders`` returns the final rendered output as a string. Alternatively the method ``render`` can be used, which is a generator and returns the output piecewise.


=============
Builtin types
=============

The following object types can be created used insided templates:

*  strings

*  integers

*  floats

*  date objects

*  color objects

*  The "null" value (``None``)

*  boolean values (``True`` and ``False``)

*  lists

*  dictionaries

*  UL4 templates

Note that depending on the implementation language of the renderer additional types might be supported, e.g. a Python renderer will probably support tuples and lists and anything supporting ``__getitem__`` (or ``__iter__`` when the list is used in a loop) for lists, Java might support anything implementing the ``List`` interface (or the ``Collection`` interface if the list is used in a loop).

Objects of these types can either be passed to the template in the call to the render function, or the template can create objects of thoses types itself. The syntax for creating such a constant is very similar to Python's syntax.


The "null" constant
-------------------

The "null" constant can be referred to via ``None``.


Boolean constants
-----------------

The boolean constants can be referred to via ``True`` and ``False``.


Integer constants
-----------------

Integer constants can be written in decimal, hexadecimal, octal and binary: ``42``, ``0x2a``, ``0o52`` and ``0b101010`` all refer to the integer value 42.


Float constants
---------------

Float constants must contain a decimal point or an exponential specifier, e.g. ``42.``, ``4e23``.


String constants
----------------

Strings are delimited with single or double quotes and support all escape sequences that Python supports (except ``\N{}``). Strings constants allow ``\uXXXX`` escaping. Examples:

*  ``"abc"`` and ``'abc'``;

*  ``"'"`` and ``'\''`` are single quotes;

*  ``'"'`` and ``"\""`` are double quotes;

*  ``"\n"`` is a line feed and ``"\t"`` is a tab;

*  ``"\x61"`` and ``"\u0061"`` are lowercase "a"s;

Strings can also be delimited with triple single or double quotes like in Python. These strings support embedded line feeds.


Date constants
--------------

Date objects have a date and time including microseconds. Date constants can be created like this:

*  ``@(2008-12-24)``

*  ``@(2008-12-24T12:34)``

*  ``@(2008-12-24T12:34:56)``

*  ``@(2008-12-24T12:34:56.987654)``


Color constants
---------------

Color values are 8 bit red, green, blue and alpha values. Color constants can be created like this:

*  ``#fff``

*  ``#fff8``

*  ``#0063a8``

*  ``#0063a880``

The variants with 3 or 6 hex digits will create a color object with an alpha value of 255.


Lists
-----

Lists can be created like this:

*  ``[]``

*  ``[1, 2, 3]``

*  ``[None, 42, "foo", [False, True]]``

It is also possible to create a list with a list comprehension:

   ["(" + c.upper() + ")" for c in "hurz" if c < "u"]

This will create the list:

   ["(H)", "(R)"]

The ``if`` condition is optional, i.e.:

   ["(" + c.upper() + ")" for c in "hurz"]

will create the list:

   ["(H)", "(U)", "(R)", "(Z)"]


Dictionaries
------------

Dictionaries can be created like this:

*  ``{}``

*  ``{1: 2, 3: 4}``

*  ``{"foo": 17, "bar": 23}``

It is also possible to create a dictionary with a dictionary comprehension:

   { c.upper() : "(" + c + ")" for c in "hurz" if c < "u"}

This will create the dictionary:

   { "H": "(h)", "R": "(r)"}

The ``if`` condition is optional, i.e.:

   { c.upper() : "(" + c + ")" for c in "hurz"}

will create the dictionary:

   { "H": "(h)", "R": "(r)", "U": "(u)", "Z": "(z)"}


Sets
----

Sets can be created like this:

*  ``{/}`` (this is the empty set)

*  ``{1, 2, 3}``

*  ``{"foo", "bar"}``

The empty set also be created with the function ``set``:

   ``set()``.

It is also possible to create a set with a set comprehension:

   {c.upper() for c in "hurz" if c < "u"}

This will create the set:

   {"H", "R"}

The ``if`` condition is optional, i.e.:

   {c.upper() for c in "hurz"}

will create the dictionary:

   {"H", "R", "U", "Z"}


The ``Undefined`` object
------------------------

The object ``Undefined`` will be returned when a non-existant variable, a non-existant dictionary entry or an index that is out of range for a list/string is accessed.


=============
Template code
=============

The template code tries to mimic Python syntax as far as possible, but is limited to what is required for templates and does not allow executing arbitrary Python statements. In some spots it also borrows Javascript semantics.

``ll.ul4c`` supports the following tag types:


``print``
---------

The ``print`` tag outputs the value of a variable or any other expression. If the expression doesn't evaluate to a string it will be converted to a string first. The format of the string depends on the renderer, but should follow Python's ``str()`` output as much as possible (except that for ``None`` no output may be produced):

   <h1><?print person.lastname?>, <?print person.firstname?></h1>


``printx``
----------

The ``printx`` tag outputs the value of a variable or any other expression and escapes the characters ``<``, ``>``, ``&``, ``'`` and ``"`` with the appropriate character or entity references for XML or HTML output.


``for``
-------

The ``for`` tag can be used to loop over the items in a list, the characters in a string or the keys in a dictionary. The end of the loop body must be marked with an ``<?end for?>`` tag:

   <ul>
       <?for person in data.persons?>
           <li><?print person.lastname?>, <?person.firstname?></li>
       <?end for?>
   </ul>

In ``for`` loops variable unpacking is supported, so you can do the following:

   <?for (key, value) in dict.items()?>

if ``dict`` is a dictionary.

This unpacking can be arbitrarily nested, i.e. the following is possible too:

   <?for (i, (key, value)) in enumerate(dict.items())?>


``break``
---------

The ``break`` tag can be used to break out of the innermost running loop.


``continue``
------------

The ``continue`` tag can be used to skip the rest of the loop body of the innermost running loop.


``if``
------

The ``if`` tag can be used to output a part of the template only when a condition is true. The end of the ``if`` block must be marked with an ``<?end if?>`` tag. The truth value of an object is mostly the same as in Python:

*  ``None`` is false.

*  The integer ``0`` and the float value ``0.0`` are false.

*  Empty strings, lists and dictionaries are false.

*  ``timedelta`` and ``monthdelta`` objects for an empty timespan (i.e. ``timedelta(0, 0, 0)`` and ``monthdelta(0)``) are false.

*  ``False`` is false.

*  ``Undefined`` is false.

*  Anything else is true.

For example we can output the person list only if there are any persons:

   <?if persons?>
       <ul>
           <?for person in persons?>
               <li><?print person.lastname?>, <?person.firstname?></li>
           <?end for?>
       </ul>
   <?end if?>

``elif`` and ``else`` are supported too:

   <?if persons?>
       <ul>
           <?for person in persons?>
               <li><?print person.lastname?>, <?person.firstname?></li>
           <?end for?>
       </ul>
   <?else?>
       <p>No persons found!</p>
   <?end if?>

or:

   <?if len(persons)==0?>
       No persons found!
   <?elif len(persons)==1?>
       One person found!
   <?else?>
       <?print len(persons)?> persons found!
   <?end if?>


``code``
--------

The ``code`` tag can contain statements that define or modify variables or expressions which will be evaluated for their side effects. Apart from the assigment operator ``=``, the following augmented assignment operators are supported:

*  ``+=`` (adds a value to the variable)

*  ``-=`` (subtracts a value from the variable)

*  ``*=`` (multiplies the variable by a value)

*  ``/=`` (divides the variable by a value)

*  ``//=`` (divides the variable by a value, rounding down to the next smallest integer)

*  ``&=`` (Does a modulo operation and replaces the variable value with the result)

For example the following template will output ``40``:

   <?code x = 17?>
   <?code x += 23?>
   <?print x?>

``render``

The ``render`` tag allows one template to call other templates. The following Python code demonstrates this:

   from ll import ul4c

   # Template 1
   source1 = """\
   <?if data?>\
   <ul>
   <?for i in data?><?render itemtmpl(item=i)?><?end for?>\
   </ul>
   <?end if?>\
   """

   tmpl1 = ul4c.Template(source1)

   # Template 2
   source2 = "<li><?print xmlescape(item)?></li>\n"

   tmpl2 = ul4c.Template(source2)

   # Data object for the outer template
   data = ["Python", "Java", "Javascript", "PHP"]

   print(tmpl1.renders(itemtmpl=tmpl2, data=data))

This will output:

   <ul>
   <li>Python</li>
   <li>Java</li>
   <li>Javascript</li>
   <li>PHP</li>
   </ul>

I.e. templates can be passed just like any other object as a variable. ``<?render itemtmpl(item=i)?>`` renders the ``itemtmpl`` template and passes the ``i`` variable, which will be available in the inner template under the name ``item``.


``def``
-------

The ``def`` tag defines a new template as a variable. Usage looks like this:

   <?def quote?>
       "<?print text?>"
   <?end def?>

This defines a local variable ``quote`` that is a template object. This template can be rendered like any other template, that has been passed to the outermost template:

   <?render quote(text="foo")?>

It's also possible to include a signature in the definition of the template. This makes it possible to define default values for template variables and to call templates with positional arguments:

   <?def quote(text='foo')?>
       "<?print text?>"
   <?end def?>
   <?render quote()?> and <?render quote("bar")?>

This will output ``"foo" and "bar"``.

``*`` and ``**`` arguments are also supported:

   <?def weightedsum(*args)?>
       <?print sum(i*arg for (i, arg) in enumerate(args, 1))?>
   <?end def?>
   <?render weightedsum(17, 23, 42)?>

This will print ``189`` (i.e. ``1 * 17 + 2 * 23 + 3 * 42``).


``ul4``
-------

The ``ul4`` tag can be used to specify a name and a signature for the template itself. This overwrites the name and signature specified in the ``ul4c.Template`` constructor:

   >>> from ll import ul4c
   >>> t = ul4c.Template("<?ul4 foo(x)?><?print x?>")
   >>> t.name
   'foo'
   >>> t.signature
   <inspect.Signature object at 0x108542d30>
   >>> print(t.signature)
   (x)


``note``
--------

A ``note`` tag is a comment, i.e. the content of the tag will be completely ignored.


``whitespace``
--------------

The ``whitespace`` tag can be used to overwrite the handling of whitespace in the template. For more info see the chapter on whitespace handling at the end.


Nested scopes
-------------

UL4 templates support lexical scopes. This means that a template that is defined (via ``<?def?>``) inside another template has access to the local variables of the outer template. The inner template sees the state of the variables at the point in time when the ``<?def?>`` tag was executed (this does not include the inner template itself or any variable defined later). The following example will output ``1``:

   <?code i = 1?>
   <?def x?>
       <?print i?>
   <?end def?>
   <?code i = 2?>
   <?render x()?>

However the state that the template sees is a "shallow" copy of the state of the variables at the point in time when the inner template was defined. So:

   <?code i = [1]?>
   <?def x?>
       <?print i?>
   <?end def?>
   <?code i.append(2)?>
   <?render x()?>

does output ``[1, 2]``.


Expressions
-----------

``ll.ul4c`` supports many of the operators supported by Python. The following subchapters describe all expression/operators that UL4 supports and are ordered from highest precedence to lowest.


Generator expressions
"""""""""""""""""""""

UL4 supports generator expressions with look like list comprehensions without the square brackets. Generator expression do not create lists in memory but instead return an iterable that can be iterated once. Function and methods that require an iterable argument can directly consume such iterables:

   <?print ", ".join("(" + c + ")" for c in "gurk")?>

will output:

   (g), (u), (r), (k)

Outside of function/method arguments (or when more that one argument is passed) parentheses are required around generator expressions:

   <?code ge = ("(" + c + ")" for c in "gurk")?>
   <?print ", ".join(ge)?>


Index/slice access
""""""""""""""""""

Index and slice access is available for all container types, i.e. in the expression ``a[b]`` the following type combinations are supported:

*  string, integer: Returns the ``b``th character from the string ``a``. Note that negative ``b`` values are supported and are relative to the end, so ``a[-1]`` is the last character.

*  list, integer: Returns the ``b``th list entry of the list ``a``. Negative ``b`` values are supported too.

*  dict, string: Return the value from the dictionary ``a`` corresponding to the key ``b``. Note that some implementations might support keys other than strings too. (The Python and Java implementations do for example. The Javascript implementation does too, if ``Map`` is supported.)

If the specified key doesn't exist or the index is out of range for the string or list, a special "undefined" object is returned.

Slices are also supported (for list and string objects). As in Python one or both of the indexes may be missing to start at the first or end after the last character/item. Negative indexes are relative to the end. Indexes that are out of bounds are simply clipped:

*  ``<?print "Hello, World!"[7:-1]?>`` prints ``World``.

*  ``<?print "Hello, World!"[:-8]?>`` prints ``Hello``.


Attribute access
""""""""""""""""

For string keys it's also possible to access dictionary entries via the attribute access operator ``.``, i.e. ``foo.key`` is the same as ``foo["key"]`` if ``foo`` is a dictionary.


Function calls
""""""""""""""

A function call in UL4 looks like this: ``date(2014, 10, 9, 17, 29)``. (this returns the date object ``@(2014-10-09T17:29)``). Some of the trailing arguments in a function call might be optional and have default values. For example the first three arguments for the ``date`` function (``year``, ``month`` and ``day``) are required, the remaining four arguments (``hour``, ``minute``, ``second`` and ``microsecond``) are optional and default to ``0``.

Parameter values can also be passed via keyword arguments, i.e. ``date(2014, 10, 9)`` could also be written as ``date(day=9, month=10, year=2014)``.

Furthermore Python's ``*`` and ``**`` syntax is supported for passing additional positional or keyword arguments. For example:

   <?code args = [2014, 10, 9, 17, 29]?>
   <?code d = date(*args)?>

is the same as:

   <?code d = date(2014, 10, 9, 17, 29)?>

The same can also be done with a keyword dictionary and the ``**`` syntax:

   <?code kwargs = {"day": 9, "month": 10, "year": 2014, "hour": 17: "minute": 29}?>
   <?code d = date(**kwargs)?>

Of course it's also possible to mix argument passing mechanics:

   <?code d = date(2014, *[10, 9], **{"hour": 17, "minute": 29})?>

or:

   <?code d = date(2014, month=10, day=9, **{'hour': 17, 'minute': 29})?>

However the ``*`` and ``**`` arguments can only be use at the end of the argument list and positional arguments must always be before keyword arguments.

A list of builtin functions can be found in a later chapter.


Unary operators
"""""""""""""""


Arithmetic negation
'''''''''''''''''''

The unary operator ``-`` inverts the sign of its operand, which must be an integer, float of boolean value:

   <?code x = 42?><?print -x?>

prints ``-42``. For ``-`` boolean values are treated as the numbers ``0`` and ``1``, i.e.:

   <?code x = True?><?print -x?>

prints ``-1``.


Binary negation
'''''''''''''''

The unary operator ``~`` inverts the bits of an integer or boolean value. Non-negative numbers are interpreted as having an unlimited number of leading ``0`` bits and negative numbers are interpreted as having an unlimited number of leading ``1`` bits. The means that ``~x`` will be negative if ``x`` is non-negative and vice versa.


Multiplicative binary operators
"""""""""""""""""""""""""""""""


Multiplication
''''''''''''''

The multiplication operator ``*`` returns the arithmetic product of its operands (which must be integer, float or boolean values). Furthermore it's possible to multiply a sequence (i.e. a string or list) with a non-negative integer to get a new sequences that repeats the items of the original sequence a number of times, e.g. ``"foo" * 2`` returns ``"foofoo"`` and ``[1, 2, 3] * 3`` return ``[1, 2, 3, 1, 2, 3, 1, 2, 3]``. Multiplying with ``0`` returns an empty string or list.


True division
'''''''''''''

The true division operator ``/`` returns the quotient of its operands (which must be integer, float or boolean values). The result is always a float value. ``1/2`` returns ``0.5``.


Floor division
''''''''''''''

The float division operator ``//`` returns the quotient of its operands (which must be integer, float or boolean values) rounded down to an integer. If any of the operands is a float the result is a float too, otherwise it's an integer.

``1//2`` returns ``0``.


Modulo
''''''

The modulo operator ``%`` returns the remainder from the division of the first operand by the second, e.g. ``15 % 7`` returns ``1``.


Additive binary operators
"""""""""""""""""""""""""


Addition
''''''''

The addition operator ``+`` returns the sum of its operands (which must be integer, float or boolean values). Furthermore sequences of the same type can be added, so ``"foo" + "bar"`` returns ``"foobar"`` and ``[1, 2] + [3, 4]`` returns ``[1, 2, 3, 4]``.


Substraction
''''''''''''

The substraction operator ``-`` returns the difference of its operands (which must be integer, float or boolean values).


Bit shift operators
"""""""""""""""""""


Binary left shift operator
''''''''''''''''''''''''''

The binary left shift operator ``<<`` shifts the bits of its first operand (an integer or boolean) to the left by the number of positions given by the second operand (which must also be an integer or boolean).


Binary right shift operator
'''''''''''''''''''''''''''

The binary right shift operator ``>>`` shifts the bits of its first operand (an integer or boolean) to the right by the number of positions given by the second operand (which must also be an integer or boolean).


Binary bitwise and operator
"""""""""""""""""""""""""""

The bitwise and operator ``&`` returns the bitwise "and" combination of its operands (which must be integer of boolean values). E.g. ``6 & 3`` returns ``2``.

As with the unary operator ``~``, negative numbers are interpreted as having an unlimited number of leading ``1`` bits.


Binary bitwise exclusive or operator
""""""""""""""""""""""""""""""""""""

The bitwise exclusive or operator ``^`` returns the bitwise exclusive "or" combination of its operands (which must be integer of boolean values). E.g. ``6 ^ 3`` returns ``5``.

Negative numbers are again interpreted as having an unlimited number of leading ``1`` bits.


Binary bitwise inclusive or operator
""""""""""""""""""""""""""""""""""""

The bitwise inclusive or operator ``|`` returns the bitwise inclusive "or" combination of its operands (which must be integer of boolean values). E.g. ``6 | 3`` returns ``7``.

Negative numbers are again interpreted as having an unlimited number of leading ``1`` bits.


Binary comparison operators
"""""""""""""""""""""""""""

The comparison operators ``==``, ``!=``, ``<``, ``<=``, ``>`` and ``>=`` compare the value of the two operands. ``==`` and ``!=`` support comparison of all types of object. All others support comparsison of "compatible" objects, which means all "number" objects (integer, float and boolean) can be compared with each other, all other objects can only be compared to objects of the same type.


Identify comparison operators
"""""""""""""""""""""""""""""

The comparison operators ``is`` and ``is not`` test whether both operands refer to the same object or not.

Note that the behaviour of these operators for "atomic" immutable objects (like integers, floats and strings) is implementation defined.


Containment tests
"""""""""""""""""


The ``in`` operator
'''''''''''''''''''

The ``in`` operator test whether the first operand is contained in the second operand. In the expression ``a in b`` the following type combinations are supported:

*  string, string: Checks whether ``a`` is a substring of ``b``.

*  any object, list: Checks whether the object ``a`` is in the list ``b`` (comparison is done by value not by identity)

*  string, dict: Checks whether the key ``a`` is in the dictionary ``b``. (Note that some implementations might support keys other than strings too. E.g. Python and Java do, Javascript doesn't.)


The ``not in`` operator
'''''''''''''''''''''''

The ``not in`` operator returns the inverted result of the ``in`` operator, i.e. it tests whether the first operand is not contained in the second operand.


Boolean negation
""""""""""""""""

The unary operator ``not`` inverts the truth value of its operand. I.e. ``not x`` is ``True`` for ``None``, ``False``, the undefined value, ``0``, ``0.0``, empty lists, strings, dictionaries and other empty container and ``False`` for everything else.


Boolean "and" operator
""""""""""""""""""""""

The binary operator ``and`` returns whether both of its operands are true. It work like in Python by short-circuiting operand evaluation, i.e. if the result is clear from the first operand the seconds won't be evaluated.

Furthermore ``and`` always return one of the operands.

So ``a and b`` first evaluates ``a``; if ``a`` is false, its value is returned; otherwise, ``b`` is evaluated and the resulting value is returned.


Boolean "or" operator
"""""""""""""""""""""

The binary operator ``or`` returns whether any of it's operands is true. Like ``and`` evaluation is short-circuited and one of the operands is returned.

For example, the following code will output the ``data.title`` object if it's true, else ``data.id`` will be output:

   <?printx data.title or data.id?>


Conditional expressions
"""""""""""""""""""""""

The conditional expression (also called an "inline if") ``a if c else b`` first evaluates the condition ``c``. If it is true ``a`` is evaluated and returned else ``b`` is evaluated and returned.


Functions
---------

``ll.ul4c`` supports a number of functions.


``now``
"""""""

``now()`` returns the current date and time as a date object.


``utcnow``
""""""""""

``utcnow()`` returns the current date and time as a date object in UTC.


``date``
""""""""

``date()`` creates a date object from the parameter passed in. ``date()`` supports from three parameters (``year``, ``month``, ``day``) upto seven parameters (``year``, ``month``, ``day``, ``hour``, ``minute``, ``second``, ``microsecond``).


``timedelta``
"""""""""""""

``timedelta`` returns an object that represents a timespan. ``timedelta`` allows from zero to three arguments specifying the numbers of days, seconds and microseconds. Passing negative values or values that are out of bounds (e.g. 24*60*60+1 seconds) is allowed. Arguments default to 0, i.e. ``timedelta()`` returns the timespan for "0 days, 0 seconds, 0 microseconds". In a boolean context this object is treated as false (i.e. ``bool(timedelta()))`` returns ``False``). The following arithmetic operations are supported:

*  ``date`` + ``timedelta``

*  ``date`` - ``timedelta``

*  ``timedelta`` + ``timedelta``

*  ``timedelta`` - ``timedelta``

*  ``number`` * ``timedelta``

*  ``timedelta`` * ``number``

*  ``timedelta`` / ``number``

*  ``timedelta`` // ``int``


``monthdelta``
""""""""""""""

``monthdelta`` returns an object that represents a timespan of a number of months. ``monthdelta`` allows zero or one arguments. With zero arguments ``monthdelta`` returns the timespan for "0 months". In a boolean context this object is treated as false (i.e. ``bool(monthdelta()))`` or ``bool(monthdelta(0)))`` return ``False``). The following arithmetic operations are supported:

*  ``date`` + ``monthdelta``

*  ``date`` - ``monthdelta``

*  ``monthdelta`` + ``monthdelta``

*  ``monthdelta`` - ``monthdelta``

*  ``int`` * ``monthdelta``

*  ``monthdelta`` // ``int``

For operations involving ``date`` objects, if the resulting day falls out of the range of valid days for the target month, the last day for the target month will be used instead, i.e. ``<?print @(2000-01-31) + monthdelta(1)?>`` prints ``2000-02-29 00:00:00``.


``isundefined``
"""""""""""""""

``isundefined(foo)`` returns ``True`` if ``foo`` is ``Undefined``, else ``False`` is returned:

   data is <?if isundefined(data)?>undefined<?else?>defined<?end if?>!


``isdefined``
"""""""""""""

``isdefined(foo)`` returns ``False`` if ``foo`` is ``Undefined``, else ``True`` is returned:

   data is <?if isdefined(data)?>defined<?else?>undefined<?end if?>!


``isnone``
""""""""""

``isnone(foo)`` returns ``True`` if ``foo`` is ``None``, else ``False`` is returned:

   data is <?if isnone(data)?>None<?else?>something else<?end if?>!


``isbool``
""""""""""

``isbool(foo)`` returns ``True`` if ``foo`` is ``True`` or ``False``, else ``False`` is returned.


``isint``
"""""""""

``isint(foo)`` returns ``True`` if ``foo`` is an integer object, else ``False`` is returned.


``isfloat``
"""""""""""

``isfloat(foo)`` returns ``True`` if ``foo`` is a float object, else ``False`` is returned.


``isstr``
"""""""""

``isstr(foo)`` returns ``True`` if ``foo`` is a string object, else ``False`` is returned.


``isdate``
""""""""""

``isdate(foo)`` returns ``True`` if ``foo`` is a date object, else ``False`` is returned.


``istimedelta``
"""""""""""""""

``istimedelta(foo)`` returns ``True`` if ``foo`` is a timedelta object, else ``False`` is returned.


``ismonthdelta``
""""""""""""""""

``ismonthdelta(foo)`` returns ``True`` if ``foo`` is a monthdelta object, else ``False`` is returned.


``islist``
""""""""""

``islist(foo)`` returns ``True`` if ``foo`` is a list object, else ``False`` is returned.


``isdict``
""""""""""

``isdict(foo)`` returns ``True`` if ``foo`` is a dictionary object, else ``False`` is returned.


``iscolor``
"""""""""""

``iscolor(foo)`` returns ``True`` if ``foo`` is a color object, else ``False`` is returned.


``istemplate``
""""""""""""""

``istemplate(foo)`` returns ``True`` if ``foo`` is a template object, else ``False`` is returned.


``bool``
""""""""

``bool(foo)`` converts ``foo`` to an boolean. I.e. ``True`` or ``False`` is returned according to the truth value of ``foo``. Calling ``bool`` without arguments returns ``False``.


``int``
"""""""

``int(foo)`` converts ``foo`` to an integer. ``foo`` can be a string, a float, a boolean or an integer. ``int`` can also be called with two arguments. In this case the first argument must be a string and the second is the number base for the conversion. Calling ``int`` without arguments returns ``0``.


``float``
"""""""""

``float(foo)`` converts ``foo`` to a float. ``foo`` can be a string, a float, a boolean or an integer. Calling ``float`` without arguments returns ``0.0``.


``str``
"""""""

``str(foo)`` converts ``foo`` to a string. If ``foo`` is ``None`` or ``Undefined`` the result will be the empty string. For lists and dictionaries the exact format is undefined, but should follow Python's repr format. For color objects the result is a CSS expression (e.g. ``"#fff"``). Calling ``str`` without arguments returns the empty string.


``repr``
""""""""

``repr(foo)`` converts ``foo`` to a string representation that is useful for debugging proposes. The output in most cases looks that the UL4 constant that could be used to recreate the object.


``list``
""""""""

``list(foo)`` converts ``foo`` to a list. This works for lists, strings and all iterable objects. Calling ``list`` without arguments returns an empty list.


``set``
"""""""

``set(foo)`` converts ``foo`` to a set. This works for lists, strings and all iterable objects. Calling ``set`` without arguments returns an empty set.


``slice``
"""""""""

``slice`` returns a slice from a sequence or iterator. You can either pass the stop index (i.e. ``slice(foo, 10)`` is an iterator over the first 10 items from ``foo``), or a start and stop index (``slice(foo, 10, 20)`` return the 11th upto to 20th item from ``foo``) or a start and stop index and a step size. If given start and stop must be non-negative and step must be positive.


``asjson``
""""""""""

``asjson(foo)`` returns a JSON representation of the object ``foo``. (Date objects, color objects and templates are not supported by JSON, but ``asjson`` will output the appropriate Javascript code for those objects).


``fromjson``
""""""""""""

``fromjson(foo)`` decodes the JSON string ``foo`` and returns the resulting object. (Date objects, color objects and templates are not supported by ``fromjson``).


``asul4on``
"""""""""""

``asul4on(foo)`` returns the UL4ON representation of the object ``foo``.


``fromul4on``
"""""""""""""

``fromul4on(foo)`` decodes the UL4ON string ``foo`` and returns the resulting object.


``len``
"""""""

``len(foo)`` returns the length of a string, or the number of items in a list or dictionary.


``any``
"""""""

``any(foo)`` returns ``True`` if any of the items in the iterable ``foo`` is true. Otherwise ``False`` is returns. If ``foo`` is empty ``False`` is returned.


``all``
"""""""

``all(foo)`` returns ``True`` if all of the items in the iterable ``foo`` are true. Otherwise ``False`` is returns. If ``foo`` is empty ``True`` is returned.


``enumerate``
"""""""""""""

Enumerates the items of the argument (which must be iterable, i.e. a string, a list or dictionary) and for each item in the original iterable returns a two item list containing the item position and the item itself. For example the following code:

   <?for (i, c) in enumerate("foo")?>
       (<?print c?>=<?print i?>)
   <?end for?>

prints:

   (f=0)(o=1)(o=2)


``isfirstlast``
"""""""""""""""

Iterates through items of the argument (which must be iterable, i.e. a string, a list or dictionary) and gives information about whether the item is the first and/or last in the iterable. For example the following code:

   <?for (first, last, c) in isfirstlast("foo")?>
       <?if first?>[<?end if?>
       (<?print c?>)
       <?if last?>]<?end if?>
   <?end for?>

prints:

   [(f)(o)(o)]


``isfirst``
"""""""""""

Iterates through items of the argument (which must be iterable, i.e. a string, a list or dictionary) and gives information about whether the item is the first in the iterable. For example the following code:

   <?for (first, c) in isfirst("foo")?>
       <?if first?>[<?end if?>
       (<?print c?>)
   <?end for?>

prints:

   [(f)(o)(o)


``islast``
""""""""""

Iterates through items of the argument (which must be iterable, i.e. a string, a list or dictionary) and gives information about whether the item is the last in the iterable. For example the following code:

   <?for (last, c) in islast("foo")?>
       (<?print c?>)
       <?if last?>]<?end if?>
   <?end for?>

prints:

   (f)(o)(o)]


``enumfl``
""""""""""

This function is a combination of ``enumerate`` and ``isfirstlast``. It iterates through items of the argument (which must be iterable, i.e. a string, a list or dictionary) and gives information about whether the item is the first and/or last in the iterable and its position. For example the following code:

   <?for (index, first, last, c) in enumfl("foo")?>
       <?if first?>[<?end if?>
       (<?print c?>=<?print index?>)
       <?if last?>]<?end if?>
   <?end for?>

prints:

   [(f=0)(o=1)(o=2)]


``first``
"""""""""

``first`` returns the first element produced by an iterable object. If the iterable is empty the default value (which is the second parameter and defaults to ``None``) is returned.


``last``
""""""""

``last`` returns the last element produced by an iterable object. If the iterable is empty the default value (which is the second parameter and defaults to ``None``) is returned.


``sum``
"""""""

``sum`` returns the sum of the number from the iterable passed in. The second parameter is the start value (i.e. the value that will be added to the total sum) and defaults to 0. For example the template ``<?print sum(range(101))?>`` will output ``5050``.


``xmlescape``
"""""""""""""

``xmlescape`` takes a string as an argument. It returns a new string where the characters ``&``, ``<``, ``>``, ``'`` and ``"`` have been replaced with the appropriate XML entity or character reference. For example:

   <?print xmlescape("<'foo' & 'bar'>")?>

prints:

   &lt;&#39;foo&#39; &amp; ;&#39;bar&#39&gt;

If the argument is not a string, it will be converted to a string first.

``<?printx foo?>`` is a shortcut for ``<?print xmlescape(foo)?>``.


``min``
"""""""

``min`` returns the minimum value of its two or more arguments. If it's called with one argument, this argument must be iterable and ``min`` returns the minimum value of this argument.


``max``
"""""""

``max`` returns the maximum value of its two or more arguments. If it's called with one argument, this argument must be iterable and ``max`` returns the maximum value of this argument.


``sum``
"""""""

``sum`` returns the sum of the values in the passed in iterable. The second argument specifies the starting value (defaulting to ``0``).


``sorted``
""""""""""

``sorted`` returns a sorted list with the items from its argument. For example:

   <?for c in sorted('abracadabra')?><?print c?><?end for?>

prints:

   aaaaabbcdrr

Supported arguments are iterable objects, i.e. strings, lists, dictionaries and colors.


``chr``
"""""""

``chr(x)`` returns a one-character string containing the character with the code point ``x``. ``x`` must be an integer. For example ``<?print chr(0x61)?>`` outputs ``a``.


``ord``
"""""""

This is the inverse function to ``chr`` The argument for ``ord`` must be a one-character string. ``ord`` returns the code point of that character as an integer. For example ``<?print ord('a')?>`` outputs ``97``.


``hex``
"""""""

Return the hexadecimal representation of the integer argument (with a leading ``0x``). For example ``<?print hex(42)?>`` outputs ``0x2a``.


``oct``
"""""""

Return the octal representation of the integer argument (with a leading ``0o``). For example ``<?print oct(42)?>`` outputs ``0o52``.


``bin``
"""""""

Return the binary representation of the integer argument (with a leading ``0b``). For example ``<?print bin(42)?>`` outputs ``0b101010``.


``range``
"""""""""

``range`` returns an object that can be iterated and will produce consecutive integers up to the specified argument. With two arguments the first is the start value and the second is the stop value. With three arguments the third one is the step size (which can be negative). For example the following template:

   <?for i in range(4, 10, 2)?>(<?print i?>)<?end for?>

outputs:

   (4)(6)(8)


``type``
""""""""

``type`` returns the type of the object as a string. Possible return values are ``"undefined"``, ``"none"``, ``"bool"``, ``"int"``, ``"float"``, ``"str"``, ``"list"``, ``"dict"``, ``"date"``, ``"timedelta"``, ``"monthdelta"``, ``"color"``, ``"template"`` and ``"function"``. (If the type isn't recognized ``None`` is returned.)


``rgb``
"""""""

``rgb`` returns a color object. It can be called with

*  three arguments, the red, green and blue values. The alpha value will be set to 255;

*  four arguments, the red, green, blue and alpha values.

Arguments are treated as values from 0 to 1 and will be clipped accordingly. For example:

   <?print rgb(1, 1, 1)?>

prints ``#fff```.


``random``
""""""""""

``random()`` returns a random float value between 0 (included) and 1 (excluded).


``randrange``
"""""""""""""

``randrange(start, stop, step)`` returns a random integer value between ``start`` (included) and ``stop`` (excluded). ``step`` specifies the step size (i.e. when ``r`` is the random value, ``(r-start) % step`` will always be ``0``). ``step`` and ``start`` can be omitted.


``randchoice``
""""""""""""""

``randchoice(seq)`` returns a random item from the sequence ``seq``.


Methods
-------

Objects in ``ll.ul4c`` support some methods too (depending on the type of the object).


``upper``
"""""""""

The ``upper`` method of strings returns an uppercase version of the string for which it's called:

   <?print 'foo'.upper()?>

prints:

   FOO


``lower``
"""""""""

The ``lower`` method of strings returns an lowercase version of the string for which it's called.


``capitalize``
""""""""""""""

The ``capitalize`` method of strings returns a copy of the string with its first letter capitalized.


``startswith``
""""""""""""""

``x.startswith(y)`` returns ``True`` if the string ``x`` starts with the string ``y`` and ``False`` otherwise.


``endswith``
""""""""""""

``x.endswith(y)`` returns ``True`` if the string ``x`` ends with the string ``y`` and ``False`` otherwise.


``strip``
"""""""""

The string method ``strip`` returns a copy of the string with leading and trailing whitespace removed. If an argument ``chars`` is given and not ``None``, characters in ``chars`` will be removed instead.


``lstrip``
""""""""""

The string method ``lstrip`` returns a copy of the string with leading whitespace removed. If an argument ``chars`` is given and not ``None``, characters in ``chars`` will be removed instead.


``rstrip``
""""""""""

The string method ``rstrip`` returns a copy of the string with trailing whitespace removed. If an argument ``chars`` is given and not ``None``, characters in ``chars`` will be removed instead.


``split``
"""""""""

The string method ``split`` splits the string into separate "words" and returns the resulting list. Without any arguments, the string is split on whitespace characters. With one argument the argument specifies the separator to use. The second optional argument specifies the maximum number of splits to do.


``rsplit``
""""""""""

The string method ``rsplit`` works like ``split``, except that splitting starts from the end (which is only relevant when the maximum number of splits is given).


``find``
""""""""

This method searches for a substring of the string or an item in a list and returns the position of the first appearance of the substring/item or -1 if the string/item can't be found. For example ``"foobar".find("bar")`` returns 3. The optional second and third argument specify the start and end position for the search.


``rfind``
"""""""""

This method works like ``find`` but searches from the end.


``replace``
"""""""""""

The string method ``replace`` has two arguments. It returns a new string where each occurrence of the first argument is replaced by the second argument, i.e. ``"abracadabra".replace("ab", "ba")`` returns ``"baracadbara"``


``get``
"""""""

``get`` is a dictionary method. ``d.get(k, v)`` returns ``d[k]`` if the key ``k`` is in ``d``, else ``v`` is returned. If ``v`` is not given, it defaults to ``None``.


``join``
""""""""

``join`` is a string method. It returns a concatentation of the strings in the argument sequence with the string itself as the separator, i.e.:

   <?print "+".join("1234")?>

outputs:

   1+2+3+4


``renders``
"""""""""""

The ``renders`` method of template objects renders the template and returns the output as a string. The parameter can be passed via keyword argument or via the ``**`` syntax:

   <?code output = template.renders(a=17, b=23)?>
   <?code data = {'a': 17, 'b': 23)?>
   <?code output = template.renders(**data)?>


``isoformat``
"""""""""""""

``isoformat`` is a date method. It returns the date object in ISO 8601 format, i.e.:

   <?print now().isoformat()?>

might output:

   2010-02-22T18:30:29.569639


``mimeformat``
""""""""""""""

``mimeformat`` is a date method. It returns the date object in MIME format (assuming the date object is in UTC), i.e.:

   <?print utcnow().mimeformat()?>

might output:

   Mon, 22 Feb 2010 17:38:40 GMT


``day``, ``month``, ``year``, ``hour``, ``minute``, ``second``, ``microsecond``, ``weekday``
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

Those methods are date methods. They return a specific attribute of a date object. For example the following reproduces the ``mimeformat`` output from above (except for the linefeeds of course):

   <?code weekdays = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']?>
   <?code months = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']?>
   <?code t = @(2010-02-22T17:38:40.123456)?>
   <?print weekdays[t.weekday()]?>,
   <?print format(t.day(), '02')?>
   <?print months[t.month()-1]?>
   <?print format(t.year(), '04')?>
   <?print format(t.hour(), '02')?>:
   <?print format(t.minute(), '02')?>:
   <?print format(t.second(), '02')?>.
   <?print format(t.microsecond(), '06')?> GMT


``week``
""""""""

``week`` is a date method. This method returns the week number of the year. It supports one argument: the weekday number that should be considered the start day of the week (0 for Monday, ... 6 for Sunday). All days in a new year preceding the first week start day are considered to be in week 0. The week start day defaults to 0 (Monday).


``yearday``
"""""""""""

``yearday`` is a date method. It returns the number of days since the beginning of the year, so:

   <?print @(2010-01-01).yearday()?>

prints ``1`` and:

   <?print @(2010-12-31).yearday()?>

prints ``365``.


``append``
""""""""""

``append`` is a list method. It adds its arguments to the end of the list for which it is called:

   <?code v = [1, 2]?>
   <?code v.append(3, 4)?>
   <?print v?>

prints ``[1, 2, 3, 4]``.


``insert``
""""""""""

``insert`` is a list method. Its first argument in the insert position, the remaining arguments are the items that will be inserted at that position, so:

   <?code v = [1, 4]?>
   <?code v.insert(1, 2, 3)?>
   <?print v?>

prints ``[1, 2, 3, 4]``.


``pop``
"""""""

``pop`` is a list method. It removes the last item of the list and returns it. If an index is passed the item at that position is removed and returned. A negative index is treated as relative to the end of the list.


``update``
""""""""""

``update`` is a dictionary method. It supports an arbitrary number of positional and keyword arguments. Each positional argument may be a dictionary, all the items in the dictionary will be copied to the target dictionary. A positional argument may also be an iterable of ``(key, value)`` pairs. These will also be copied to the target dictionary. After each positional argument is copied over in a last step the keyword arguments will be copied to the target dictionary.


======================
Templates as functions
======================

UL4 templates can be used as functions too. Calling a template as a function will ignore any output from the template. The return value will be the value of the first ``<?return?>`` tag encountered:

   from ll import ul4c

   code = """
       <?for item in data?>
           <?if "i" in item?>
               <?return item?>
           <?end if?>
       <?end for?>
   """

   function = ul4c.Template(code)

   output = function(data=["Python", "Java", "Javascript", "PHP"]))

With this, ``output`` will be the string ``"Javascript"``.

When no ``<?return?>`` tag is encountered, ``None`` will be returned.

When a ``<?return?>`` tag is encountered when the template is used as a template, output will simply stop and the return value will be ignored.


===================
Exposing attributes
===================

It is possible to expose attributes of an object to UL4 templates. This is done by setting the class attribute ``ul4attrs``:

   from ll import ul4c

   class Person:
       ul4attrs = {"firstname", "lastname"}

       def __init__(self, firstname, lastname, age):
           self.firstname = firstname
           self.lastname = lastname
           self.age = age

   p = Person("John", "Doe", 42)

   template = ul4c.Template("<?print p.lastname?>, <?print p.firstname?>")
   print(template.renders(p=p))

This will output ``Doe, John``.

Attributes not in ``ul4attrs`` will not be visible:

   template = ul4c.Template("<?print type(p.age)?>")
   print(template.renders(p=p))

This will output ``undefined``. Exposing attributes via ``ul4attrs`` also makes it possible to use dictionary access to the object, i.e. iterating over the object, using ``in`` and ``not in`` tests and using the methods ``items`` and ``values``.


================
Exposing methods
================

It is also possible to expose methods of an object to UL4 templates. This is done by including the method name in the ``ul4attrs`` class attribute:

   from ll import ul4c

   class Person:
       ul4attrs = {"fullname"}

       def __init__(self, firstname, lastname):
           self.firstname = firstname
           self.lastname = lastname

       def fullname(self):
           return self.firstname + " " + self.lastname

   p = Person("John", "Doe")

   template = ul4c.Template("<?print p.fullname()?>")
   print(template.renders(p=p))

This will output ``John Doe``.

Furthermore it's possible to specify that the method needs access to the rendering context (which stores the local variables and the UL4 call stack):

   class Person:
       ul4attrs = {"fullname", "varcount"}

       @ul4c.withcontext
       def varcount(self):
           return len(context.vars)


=================
Custom attributes
=================

To customize getting and setting object attributes from UL4 templates the methods ``ul4getattr`` and ``ul4setattr`` can be implemented:

   from ll import ul4c

   class Person:
       ul4attrs = {"firstname", "lastname"}

       def __init__(self, firstname, lastname, age):
           self.firstname = firstname
           self.lastname = lastname
           self.age = age

       def ul4getattr(self, name):
           return getattr(self, name).upper()

   p = Person("John", "Doe", 42)

   template = ul4c.Template("<?print p.lastname?>, <?print p.firstname?>")
   print(template.renders(p=p))

This will output ``DOE, JOHN``.

If the object has an attribute ``ul4attrs`` ``ul4getattr`` will only be called for the attributes in ``ul4attrs``, otherwise ``ul4getattr`` will be called for all attributes (and should raise an ``AttributeError`` for non-existant attributes)

Attributes can be made writable by implemention the method ``ul4setattr``:

   from ll import ul4c

   class Person:
       ul4attrs = {"firstname", "lastname"}

       def __init__(self, firstname, lastname, age):
           self.firstname = firstname
           self.lastname = lastname
           self.age = age

       def ul4setattr(self, name, value):
           return setattr(self, name, value.upper())

   p = Person("John", "Doe", 42)

   template = ul4c.Template("<?code p.lastname = 'Doe'?><?print p.lastname?>, <?print p.firstname?>")
   print(template.renders(p=p))

This will output ``DOE, John``.

If the object has an attribute ``ul4attrs`` ``ul4setattr`` will only be called for the attributes in ``ul4attrs``, otherwise ``ul4setattr`` will be called for all attributes (and should raise an ``AttributeError`` for non-existant or readonly attributes)

Without a ``ul4setattr`` method, attributes will never be made writable.


==========
Delimiters
==========

It is possible to specify alternative delimiters for the template tags:

   >>> from ll import ul4c
   >>> t = ul4c.Template(
   ...     "{{for i in range(10)}}{{print i}};{{end for}}",
   ...     startdelim="{{",
   ...     enddelim="}}"
   ... )
   >>> t.renders()
   '0;1;2;3;4;5;6;7;8;9;'


==========
Whitespace
==========

Normally the literal text between template tags will be output as it is. This behaviour can be changed by passing a different value to the ``whitespace`` parameter in the constructor. The possible values are:

``"keep"``
   The default behaviour: literal text with be output as it is.

``"strip"``
   Linefeeds and the following indentation in literal text will be ignored:

      >>> from ll import ul4c
      >>> t = ul4c.Template("""
      ...     <?for i in range(10)?>
      ...         <?print i?>
      ...         ;
      ...     <?end for?>
      ... """, whitespace="strip")
      >>> t.renders()
      '0;1;2;3;4;5;6;7;8;9;'

   However trailing whitespace at the end of the line will still be honored.

``"smart"``
   If a line contains only indentation and one tag that isn't a ``print``, ``printx`` or ``render`` tag, the indentation and the linefeed after the tag will be stripped from the text. Furthermore the additional indentation that might be introduced by a ``for``, ``if``, ``elif``, ``else`` or ``def`` block will be ignored. So for example the output of:

      <?code langs = ["Python", "Java", "Javascript"]?>
      <?if langs?>
          <?for lang in langs?>
              <?print lang?>
          <?end for?>
      <?end if?>

   will simply be:

      Python
      Java
      Javascript

   without any additional empty lines or indentation.

   Rendering a template ``B`` inside an template ``A`` will reindent the output of ``B`` to the indentation level of the ``<?render?>`` tag in the template ``A``.

It is also possible to specify the whitespace behaviour in the template itself with the ``<?whitespace?>`` tag, so:

   <?whitespace smart?>

anywhere in the template source will switch on smart whitespace handling.

A ``<?whitespace?>`` tag overwrites the ``whitespace`` parameter specified in the constructor.