lib3to2 / lib3to2 / fixes /

Base classes for features that are backwards-incompatible.

features = Features()
features.add(Feature("py3k_feature", "power< 'py3k' any* >", "2.7"))

pattern_unformatted = "%s=%s" # name=pattern, for dict lookups
message_unformatted = """
%s is only supported in Python %s and above."""

class Feature(object):
    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): = name
        self._pattern = PATTERN
        self.version = version

    def message_text(self):
        Format the above text with the name and minimum version required.
        return message_unformatted % (, self.version)

class Features(set):
    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):
        Called every time we care about the mapping of names to features.
        self.mapping = dict([(, f) for f in iter(self)])
    def PATTERN(self):
        Uses the mapping of names to features to return a PATTERN suitable
        for using the lib2to3 patcomp.
        return " |\n".join([pattern_unformatted % (, f._pattern) for f in iter(self)])

    def __getitem__(self, key):
        Implement a simple mapping to get patterns from names.
        return self.mapping[key]