Package genshi :: Package template :: Module eval :: Class Expression |

# Class Expression

    object --+
             |
          Code --+
                 |
                Expression

Evaluates Python expressions used in templates.

    >>> data = dict(test='Foo', items=[1, 2, 3], dict={'some': 'thing'})
    >>> Expression('test').evaluate(data)
    'Foo'

    >>> Expression('items[0]').evaluate(data)
    1
    >>> Expression('items[-1]').evaluate(data)
    3
    >>> Expression('dict["some"]').evaluate(data)
    'thing'

Similar to e.g. Javascript, expressions in templates can use the dot notation for attribute access to access items in mappings:

    >>> Expression('dict.some').evaluate(data)
    'thing'

This also works the other way around: item access can be used to access any object attribute:

    >>> class MyClass(object):
    ...     myattr = 'Bar'
    >>> data = dict(mine=MyClass(), key='myattr')
    >>> Expression('mine.myattr').evaluate(data)
    'Bar'
    >>> Expression('mine["myattr"]').evaluate(data)
    'Bar'
    >>> Expression('mine[key]').evaluate(data)
    'Bar'

All of the standard Python operators are available to template expressions. Built-in functions such as `len()` are also available in template expressions:

    >>> data = dict(items=[1, 2, 3])
    >>> Expression('len(items)').evaluate(data)
    3

Instance Methods
evaluate(self, data) Evaluate the expression against the given data dictionary. |
Inherited from `Code`: `__eq__`, `__getstate__`, `__hash__`, `__init__`, `__ne__`, `__repr__`, `__setstate__` Inherited from `object`: `__delattr__`, `__format__`, `__getattribute__`, `__new__`, `__reduce__`, `__reduce_ex__`, `__setattr__`, `__sizeof__`, `__str__`, `__subclasshook__`

Class Variables
| mode = ``'``eval``'``

Properties
Inherited from `Code`: `ast`, `code`, `source` Inherited from `object`: `__class__`

Method Details

### evaluate(self, data) |
Evaluate the expression against the given data dictionary. Parameters: `data` - a mapping containing the data to evaluate against Returns: the result of the evaluation