Return True if path is within sys.prefix, if we're running in a virtualenv.

    Return True if this is a path pip is allowed to modify.

    If we're not in a virtualenv, all paths are considered "local."

    If we're in a virtualenv, sys.prefix points to the virtualenv's

    prefix; only sys.prefix is considered local.

    If we're not in a virtualenv, in general we can modify anything.

    However, if the OS vendor has configured distutils to install

    somewhere other than sys.prefix (which could be a subdirectory of

    sys.prefix, e.g. /usr/local), we consider sys.prefix itself nonlocal

    and the domain of the OS vendor. (In other words, everything _other

    than_ sys.prefix is considered local.)

    if not running_under_virtualenv():

        return True

    path = normalize_path(path)

    return normalize_path(path).startswith(normalize_path(sys.prefix))

    prefix = normalize_path(sys.prefix)

    if running_under_virtualenv():

        return path.startswith(normalize_path(sys.prefix))

    else:

        from pip.locations import distutils_scheme

        if path.startswith(prefix):

            for local_path in distutils_scheme("").values():

                if path.startswith(normalize_path(local_path)):

                    return True

            return False

        else:

            return True

    Return True if given Distribution object is installed locally

    Return True if given Distribution object is installed somewhere pip

    (i.e. within current virtualenv).

    is allowed to modify.

    Always True if we're not in a virtualenv.