URL Helper for Django / Django Rest Framework

url_ex.py

# -*- coding: utf-8 -*
# 
# URL_EX : url helper to make dealing with patterns in urls easier, and prevent common issues
#   - calls .as_view() on DRF APIView instances automatically
#   - appends a leading ^
#   - appends a trailing $ the the call isn't an include()
#   - add more shortcuts and patterns as required
#
# Examples:
# urlpatterns = [
#    url_ex('accounts/:id/', GetAccountView),            => r'accounts/(?<id>\d+)/$'
#    url_ex('accounts/:id/', ..., case_sensitive=False)  => r'(?i)accounts/(?<id>\d+)/$'
# ]
#
# Patterns are one of ":shortcut" or ":name:var_type" 
# - if the variable does not have a :int (or other type at the end) we will split on "_" and use the end part
# - as the shortcut to use.  so "new_id" == "name=new_id, shortcut=id", where id is an int.
# 
# - "user/:pk/"            gets a variable named 'pk', using the 'pk' shortcut to define the data type regex
# - "user/:oldname:int/"   integer variable named "abc"
# - "user/:my_id/          variable named 'my_id', using the 'id' shortcut for the data type
# - "user/:my_id:uuid/     variable named 'my_id', but of type 'uuid'
#
from __future__ import print_function, absolute_import, unicode_literals

import re

__all__ = [
    'url_ex'
]

VAR_TYPES = dict(
    int=r'\d+',
    decimal=r'\d+(\.\d+)?',
    uuid=r'[0-9A-Fa-f]{8}-?[0-9A-Fa-f]{4}-?[1345][0-9A-Fa-f]{3}-?[0-9A-Fa-f]{4}-?[0-9A-Fa-f]{12}',
    slug=r'[-\w]+',
    hex='[0-9A-Fa-f]+',
)

VAR_SHORTCUTS = dict(
    id=VAR_TYPES['int'],
    pk=VAR_TYPES['int'],
    fk=VAR_TYPES['int'],
    slug=VAR_TYPES['slug'],
    uuid=VAR_TYPES['uuid'],
)

VARNAME = r'([a-zA-Z]\w*)'
RE_EXPLICIT = r'(:{var}:([a-z]+))'.format(var=VARNAME)
RE_SHORTCUT = r'(:{var})'.format(var=VARNAME)


def url_ex(url, view, kwargs=None, name=None, prefix='', case_sensitive=True):
    from django.conf.urls import url as djang_url

    # if the view has a function called 'as_view' which is callable, then we are probably
    # dealing with a class based view and need to call as_view first.  This should help remove
    # some cryptic errors when this is not done by the user
    if callable(getattr(view, 'as_view', None)):
        view = view.as_view()

    # Don't add a $ when including sub-views via include('my.app.urls') => (module,app,namespace)
    add_eol = not (isinstance(view, tuple) and len(view) == 3)
    url = '^{case}{url}{eol}'.format(
        url=url.lstrip(' ^\n').rstrip(' $\n'),
        eol='$' if add_eol else '',
        case="(?i)" if not case_sensitive else ""
    )

    return djang_url(_patch_url(url), view, kwargs=kwargs, name=name, prefix=prefix)

def _patch_url(url):
    new_url = _patch_typed_variables(url, original_url=url)
    new_url = _patch_shortcuts(new_url, original_url=url)
    return new_url

def _url_var(var_name, type_regex):
    """
    Creates the regex for a django URL variable
    """
    return '(?P<{name}>{regex})'.format(name=var_name, regex=type_regex)


def _patch_shortcuts(url, original_url):
    """
    Patch all short variables (the ones without an explicit data type)
    """
    found_shortcuts = re.findall(RE_SHORTCUT, url)

    var_names = [var for _, var in found_shortcuts]
    if len(var_names) != len(set(var_names)):
        raise ValueError("Duplicate variable found in url %s" % original_url)

    for full_match, var_name in found_shortcuts:
        url = _patch_single_shortcut(url, full_match, var_name, original_url)

    return url


def _patch_single_shortcut(url, full_match, var_name, original_url):
    # check for full match first (more specific) before checking for ends with, in case
    # we have two shortcuts like ('id=\d+' and my_id=r'AF\d+').
    if var_name in VAR_SHORTCUTS:
        return url.replace(full_match, _url_var(var_name, VAR_SHORTCUTS[var_name]))

    for key, regex in VAR_SHORTCUTS.iteritems():
        if var_name.endswith('_%s' % key):
            return url.replace(full_match, _url_var(var_name, regex))

    raise ValueError("Name %s is not a valid shortcut (url=%s)" % (var_name, original_url))


def _patch_typed_variables(url, original_url):
    """
    Replaces all occurances of ":var:type" found in the URL
    :type url: str
    """
    typed_vars = re.findall(RE_EXPLICIT, url)

    var_names = [n for _, n, _ in typed_vars]
    if len(var_names) != len(set(var_names)):
        raise ValueError("Duplicate typed variable found in url %s" % original_url)

    for full_match, var_name, typ in typed_vars:
        if not typ in VAR_TYPES:
            raise ValueError("Type pattern '%s' not found (url=%s)" % (typ, original_url))
        url = url.replace(full_match, _url_var(var_name, VAR_TYPES[typ]))

    return url