'Import a module and return a reference to it or None on failure.'

def _conditional_import_module(self, module_name):

    try:
        exec ('import    ' + module_name)
    except ImportError as error:
        if self._warn_on_extension_import:
            warnings.warn(('Did    a    C    extension    fail    to    compile?    %s' % error))
    return locals().get(module_name)
