django-rest-framework/rest_framework/urlpatterns.py

from django.conf.urls.defaults import url
from rest_framework.settings import api_settings


def format_suffix_patterns(urlpatterns, suffix_required=False, allowed=None):
    """
    Supplement existing urlpatterns with corresponding patterns that also
    include a '.format' suffix.  Retains urlpattern ordering.

    urlpatterns:
        A list of URL patterns.

    suffix_required:
        If `True`, only suffixed URLs will be generated, and non-suffixed
        URLs will not be used.  Defaults to `False`.

    allowed:
        An optional tuple/list of allowed suffixes.  eg ['json', 'api']
        Defaults to `None`, which allows any suffix.
    """
    suffix_kwarg = api_settings.FORMAT_SUFFIX_KWARG
    if allowed:
        if len(allowed) == 1:
            allowed_pattern = allowed[0]
        else:
            allowed_pattern = '(%s)' % '|'.join(allowed)
        suffix_pattern = r'\.(?P<%s>%s)$' % (suffix_kwarg, allowed_pattern)
    else:
        suffix_pattern = r'\.(?P<%s>[a-z]+)$' % suffix_kwarg

    ret = []
    for urlpattern in urlpatterns:
        # Form our complementing '.format' urlpattern
        regex = urlpattern.regex.pattern.rstrip('$') + suffix_pattern
        view = urlpattern._callback or urlpattern._callback_str
        kwargs = urlpattern.default_args
        name = urlpattern.name
        # Add in both the existing and the new urlpattern
        if not suffix_required:
            ret.append(urlpattern)
        ret.append(url(regex, view, kwargs, name))
    return ret