'Snapshot distributions available on a search path
Any distributions found on `search_path` are added to the environment.
`search_path` should be a sequence of ``sys.path`` items.  If not
supplied, ``sys.path`` is used.
`platform` is an optional string specifying the name of the platform
that platform-specific distributions must be compatible with.  If
unspecified, it defaults to the current platform.  `python` is an
optional string naming the desired version of Python (e.g. ``\'2.4\'``);
it defaults to the current version.
You may explicitly set `platform` (and/or `python`) to ``None`` if you
wish to map *all* distributions, not just those compatible with the
running platform or Python version.'

def __init__(self, search_path=None, platform=get_supported_platform(), python=PY_MAJOR):

    self._distmap = {}
    self._cache = {}
    self.platform = platform
    self.python = python
    self.scan(search_path)
