'Get version number of installed module, \'None\', or \'default\'
Search \'paths\' for module.  If not found, return \'None\'.  If found,
return the extracted version attribute, or \'default\' if no version
attribute was specified, or the value cannot be determined without
importing the module.  The version is formatted according to the
requirement\'s version format (if any), unless it is \'None\' or the
supplied \'default\'.'

def get_version(self, paths=None, default='unknown'):

    if (self.attribute is None):
        try:
            (f, p, i) = find_module(self.module, paths)
            if f:
                f.close()
            return default
        except ImportError:
            return None
    v = get_module_constant(self.module, self.attribute, default, paths)
    if ((v is not None) and (v is not default) and (self.format is not None)):
        return self.format(v)
    return v
