def guess_folder_vcs(folder):
    """
    Given a path for a folder on the local filesystem, see what kind of vcs
    repo it is, if any.
    """
    try:
        contents = os.listdir(folder)
        vcs_folders = ['.git', '.hg', '.svn']
        found = next((x for x in vcs_folders if x in contents), None)
        # Chop off the dot if we got a string back
        return found[1:] if found else None
    except OSError:
        return None