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# -*- test-case-name: epsilon.test.test_structlike -*-
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This module implements convenience objects for classes which have initializers
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and repr()s that describe a fixed set of attributes.
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from twisted.python import context
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_NOT_SPECIFIED = object()
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class _RecursiveReprer(object):
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This object maintains state so that repr()s can tell when they are
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recursing and not do so.
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def recursiveRepr(self, stuff, thunk=repr):
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return '%s(...)' % (stuff.__class__.__name__,)
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self.active[ID] = stuff
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def _contextualize(contextFactory, contextReceiver):
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Invoke a callable with an argument derived from the current execution
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context (L{twisted.python.context}), or automatically created if none is
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yet present in the current context.
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This function, with a better name and documentation, should probably be
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somewhere in L{twisted.python.context}. Calling context.get() and
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context.call() individually is perilous because you always have to handle
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the case where the value you're looking for isn't present; this idiom
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forces you to supply some behavior for that case.
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@param contextFactory: An object which is both a 0-arg callable and
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hashable; used to look up the value in the context, set the value in the
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context, and create the value (by being called).
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@param contextReceiver: A function that receives the value created or
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identified by contextFactory. It is a 1-arg callable object, called with
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the result of calling the contextFactory, or retrieving the contextFactory
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value = context.get(contextFactory, _NOT_SPECIFIED)
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if value is not _NOT_SPECIFIED:
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return contextReceiver(value)
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return context.call({contextFactory: contextFactory()},
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_contextualize, contextFactory, contextReceiver)
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class StructBehavior(object):
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def __init__(self, *args, **kw):
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super(StructBehavior, self).__init__()
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# Turn all the args into kwargs
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if len(args) > len(self.__names__):
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"Got %d positional arguments but expected no more than %d" %
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(len(args), len(self.__names__)))
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for n, v in zip(self.__names__, args):
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raise TypeError("Got multiple values for argument " + n)
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for n, v in zip(self.__names__[::-1], self.__defaults__[::-1]):
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for n in self.__names__:
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raise TypeError('Specify a value for %r' % (n,))
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setattr(self, n, kw.pop(n))
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raise TypeError('Got unexpected arguments: ' + ', '.join(kw))
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Generate a string representation.
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def _recordrepr(self2):
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Internal implementation of repr() for this record.
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self.__class__.__name__,
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(n, repr(getattr(self, n, None)))
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for n in self.__names__]))
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return rr.recursiveRepr(self, _recordrepr)
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return _contextualize(_RecursiveReprer, doit)
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def record(*a, **kw):
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Are you tired of typing class declarations that look like this::
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def __init__(self, a=None, b=None, c=None, d=None, e=None,
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f=None, g=None, h=None, i=None, j=None):
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Epsilon can help! That's right - for a limited time only, this function
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returns a class which provides a shortcut. The above can be simplified
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StuffInfo = record(a=None, b=None, c=None, d=None, e=None,
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f=None, g=None, h=None, i=None, j=None)
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if the arguments are required, rather than having defaults, it could be
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StuffInfo = record('a b c d e f g h i j')
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Put more formally: C{record} optionally takes one positional argument, a
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L{str} representing attribute names as whitespace-separated identifiers; it
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also takes an arbitrary number of keyword arguments, which map attribute
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names to their default values. If no positional argument is provided, the
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names of attributes will be inferred from the names of the defaults
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attributeNames = a[0].split()
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raise TypeError("Attempted to define a record with no attributes.")
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attributeNames = kw.keys()
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attributeNames.sort()
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"record must be called with zero or one positional arguments")
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# Work like Python: allow defaults specified backwards from the end
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for attributeName in attributeNames:
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default = kw.pop(attributeName, _NOT_SPECIFIED)
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if default is _NOT_SPECIFIED:
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"You must specify default values like in Python; "
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"backwards from the end of the argument list, "
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defaults.append(default)
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elif default is not _NOT_SPECIFIED:
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defaults.append(default)
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# This space left intentionally blank.
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raise TypeError("The following defaults did not apply: %r" % (kw,))
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return type('Record<%s>' % (' '.join(attributeNames),),
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dict(__names__=attributeNames,
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__defaults__=defaults))
added
removed
Epsilon/epsilon/structlike.py
