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.

    >>> foo('bar')
    Traceback (most recent call last):
        ...
    UndefinedError: "foo" not defined

    >>> foo.bar
    Traceback (most recent call last):
        ...
    UndefinedError: "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__`, `__getattribute__`, `__hash__`, `__new__`, `__reduce__`, `__reduce_ex__`, `__setattr__`

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)