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u"""
Base classes for features that are backwards-incompatible.
Usage:
features = Features()
features.add(Feature("py3k_feature", "power< 'py3k' any* >", "2.7"))
PATTERN = features.PATTERN
"""
pattern_unformatted = u"%s=%s" # name=pattern, for dict lookups
message_unformatted = u"""
%s is only supported in Python %s and above."""
class Feature(object):
u"""
A feature has a name, a pattern, and a minimum version of Python 2.x
required to use the feature (or 3.x if there is no backwards-compatible
version of 2.x)
"""
def __init__(self, name, PATTERN, version):
self.name = name
self._pattern = PATTERN
self.version = version
def message_text(self):
u"""
Format the above text with the name and minimum version required.
"""
return message_unformatted % (self.name, self.version)
class Features(set):
u"""
A set of features that generates a pattern for the features it contains.
This set will act like a mapping in that we map names to patterns.
"""
mapping = {}
def update_mapping(self):
u"""
Called every time we care about the mapping of names to features.
"""
self.mapping = dict([(f.name, f) for f in iter(self)])
@property
def PATTERN(self):
u"""
Uses the mapping of names to features to return a PATTERN suitable
for using the lib2to3 patcomp.
"""
self.update_mapping()
return u" |\n".join([pattern_unformatted % (f.name, f._pattern) for f in iter(self)])
def __getitem__(self, key):
u"""
Implement a simple mapping to get patterns from names.
"""
return self.mapping[key]