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]