genshi.template.eval.Undefined

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

# Class Undefined

    object --+
             |
            Undefined

Represents a reference to an undefined variable.

Unlike the Python runtime, template expressions can refer to an undefined variable without causing a `NameError` to be raised. The result will be an instance of the Undefined class, which is treated the same as `False` in conditions, but raise an exception on any other operation:

    >>> foo = Undefined('foo')
    >>> bool(foo)
    False
    >>> list(foo)
    []
    >>> print(foo)
    undefined

However, calling an undefined variable, or trying to access an attribute of that variable, will raise an exception that includes the name used to reference that undefined variable.

    >>> try:
    ...     foo('bar')
    ... except UndefinedError, e:
    ...     print e.msg
    "foo" not defined

    >>> try:
    ...     foo.bar
    ... except UndefinedError, e:
    ...     print e.msg
    "foo" not defined

See Also: LenientLookup

Instance Methods
__init__(self, name, owner=UNDEFINED) Initialize the object. |
__iter__(self) |
__nonzero__(self) |
__repr__(self) repr(x) |
__str__(self) str(x) |
__getitem__(self, *args, **kwargs) Raise an UndefinedError. |
__getattr__(self, *args, **kwargs) Raise an UndefinedError. |
__call__(self, *args, **kwargs) Raise an UndefinedError. |
Inherited from `object`: `__delattr__`, `__format__`, `__getattribute__`, `__hash__`, `__new__`, `__reduce__`, `__reduce_ex__`, `__setattr__`, `__sizeof__`, `__subclasshook__`

Class Variables
| __length_hint__ = `None` hash(x)

Properties
Inherited from `object`: `__class__`

Method Details

### __init__(self, name, owner=UNDEFINED) (Constructor) |
Initialize the object. Parameters: `name` - the name of the reference `owner` - the owning object, if the variable is accessed as a member Overrides: object.__init__

### __repr__(self) (Representation operator) |
repr(x) Overrides: object.__repr__ (inherited documentation)

### __str__(self) (Informal representation operator) |
str(x) Overrides: object.__str__ (inherited documentation)