is_rails_file.py

import os
import re
import platform

def is_rails_file(file_name):
    windows = platform.system() == "Windows"

    path = os.path.dirname(file_name)
    file_name = os.path.basename(file_name).lower()
    name, extension = os.path.splitext(file_name)

    if name == 'gemfile':
        return True

    result = False

    # I doubt this is the most elegant way of identifying a Rails directory structure,
    # but it does work. The idea here is to work up the tree, checking at each level for
    # the existence of config/routes.rb. If it's found, the assumption is made that it's
    # a Rails app.
    while path != '':
        if os.path.exists(os.path.join(path, 'config', 'routes.rb')):
            result = True
            break
        elif windows and re.match(r"^[A-Za-z]{1}:\\$", path) is not None:
            path = ''
        elif not windows and path == '/':
            path = ''
        else:
            path = os.path.dirname(path)

    return extension in ['.rb', '.rake'] and result