Class FeatureVariable
SubstituteBindingsI
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FeatureVariable
- Known Subclasses:
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AliasedFeatureVariable
A variable that can stand for a single feature value in a feature
structure. Each variable is defined by a unique identifier, which can be
either a case-sensitive string (for named
variables) or an integer (for numbered
variables).
Named variables are created by calling the
FeatureVariable
constructor with a string identifier. If
multiple named variables objects are created with the same identifier,
then they represent the same variable. Numbered variables are created by
calling the FeatureVariable
constructor with no arguments; a
new identifier will be automatically generated. Each new numbered
variable object is guaranteed to have a unique identifier.
Variables do not directly contain values; instead, the mapping from
variables to values is encoded externally as a set of bindings, using FeatureBindings
. If a set of bindings
assigns a value to a variable, then that variable is said to be bound with respect to
those bindings; otherwise, it is said to be unbound.
See Also: FeatureStructure
Method Summary |
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__init__ (self,
identifier)
Construct a new feature structure variable. |
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__cmp__(self,
other)
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__hash__(self)
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__repr__ (self)
Return a string representation of this feature structure variable. |
AliasedFeatureVariable
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alias (self,
variable)
Return an aliased variable that constrains this variable to be equal
to variable . |
string
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identifier (self)
Return this variable's unique identifier. |
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parse (s)
Given a string that encodes a feature variable, return that
variable. (Static method)
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(any)
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substitute_bindings (self,
bindings)
Return the value that is bound to this variable if it appears in
@bindings otherwise just return self. |
__init__(self,
identifier=None)
(Constructor)
Construct a new feature structure variable.
-
- Parameters:
identifier -
A unique identifier for this variable. Any two
FeatureVariable objects with the same identifier are
treated as the same variable.
(type=string )
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__repr__(self)
(Representation operator)
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- Returns:
-
A string representation of this feature structure variable. A
feature structure variable with identifier
x
is represented as '?x' .
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alias(self,
variable)
Return an aliased variable that constrains this variable to be equal
to variable .
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- Returns:
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AliasedFeatureVariable
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identifier(self)
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- Returns:
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This variable's unique identifier.
(type=string )
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parse(s)
Given a string that encodes a feature variable, return that
variable. This method can be used to parse both
FeatureVariables and AliasedFeatureVariables .
However, this method can not be used to parse numbered variables, since
doing so could violate the guarantee that each numbered variable object
has a unique identifier.
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