##// END OF EJS Templates
check submodules when starting the notebook server...
check submodules when starting the notebook server shows a warning (not an error) if components are out of date.

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handlers.py
931 lines | 30.5 KiB | text/x-python | PythonLexer
"""Tornado handlers for the notebook.
Authors:
* Brian Granger
"""
#-----------------------------------------------------------------------------
# Copyright (C) 2008-2011 The IPython Development Team
#
# Distributed under the terms of the BSD License. The full license is in
# the file COPYING, distributed as part of this software.
#-----------------------------------------------------------------------------
#-----------------------------------------------------------------------------
# Imports
#-----------------------------------------------------------------------------
import Cookie
import datetime
import email.utils
import hashlib
import logging
import mimetypes
import os
import stat
import threading
import time
import uuid
from tornado.escape import url_escape
from tornado import web
from tornado import websocket
try:
from tornado.log import app_log
except ImportError:
app_log = logging.getLogger()
from zmq.eventloop import ioloop
from zmq.utils import jsonapi
from IPython.config import Application
from IPython.external.decorator import decorator
from IPython.kernel.zmq.session import Session
from IPython.lib.security import passwd_check
from IPython.utils.jsonutil import date_default
from IPython.utils.path import filefind
from IPython.utils.py3compat import PY3
try:
from docutils.core import publish_string
except ImportError:
publish_string = None
#-----------------------------------------------------------------------------
# Monkeypatch for Tornado <= 2.1.1 - Remove when no longer necessary!
#-----------------------------------------------------------------------------
# Google Chrome, as of release 16, changed its websocket protocol number. The
# parts tornado cares about haven't really changed, so it's OK to continue
# accepting Chrome connections, but as of Tornado 2.1.1 (the currently released
# version as of Oct 30/2011) the version check fails, see the issue report:
# https://github.com/facebook/tornado/issues/385
# This issue has been fixed in Tornado post 2.1.1:
# https://github.com/facebook/tornado/commit/84d7b458f956727c3b0d6710
# Here we manually apply the same patch as above so that users of IPython can
# continue to work with an officially released Tornado. We make the
# monkeypatch version check as narrow as possible to limit its effects; once
# Tornado 2.1.1 is no longer found in the wild we'll delete this code.
import tornado
if tornado.version_info <= (2,1,1):
def _execute(self, transforms, *args, **kwargs):
from tornado.websocket import WebSocketProtocol8, WebSocketProtocol76
self.open_args = args
self.open_kwargs = kwargs
# The difference between version 8 and 13 is that in 8 the
# client sends a "Sec-Websocket-Origin" header and in 13 it's
# simply "Origin".
if self.request.headers.get("Sec-WebSocket-Version") in ("7", "8", "13"):
self.ws_connection = WebSocketProtocol8(self)
self.ws_connection.accept_connection()
elif self.request.headers.get("Sec-WebSocket-Version"):
self.stream.write(tornado.escape.utf8(
"HTTP/1.1 426 Upgrade Required\r\n"
"Sec-WebSocket-Version: 8\r\n\r\n"))
self.stream.close()
else:
self.ws_connection = WebSocketProtocol76(self)
self.ws_connection.accept_connection()
websocket.WebSocketHandler._execute = _execute
del _execute
#-----------------------------------------------------------------------------
# Decorator for disabling read-only handlers
#-----------------------------------------------------------------------------
@decorator
def not_if_readonly(f, self, *args, **kwargs):
if self.settings.get('read_only', False):
raise web.HTTPError(403, "Notebook server is read-only")
else:
return f(self, *args, **kwargs)
@decorator
def authenticate_unless_readonly(f, self, *args, **kwargs):
"""authenticate this page *unless* readonly view is active.
In read-only mode, the notebook list and print view should
be accessible without authentication.
"""
@web.authenticated
def auth_f(self, *args, **kwargs):
return f(self, *args, **kwargs)
if self.settings.get('read_only', False):
return f(self, *args, **kwargs)
else:
return auth_f(self, *args, **kwargs)
def urljoin(*pieces):
"""Join components of url into a relative url
Use to prevent double slash when joining subpath
"""
striped = [s.strip('/') for s in pieces]
return '/'.join(s for s in striped if s)
#-----------------------------------------------------------------------------
# Top-level handlers
#-----------------------------------------------------------------------------
class RequestHandler(web.RequestHandler):
"""RequestHandler with default variable setting."""
def render(*args, **kwargs):
kwargs.setdefault('message', '')
return web.RequestHandler.render(*args, **kwargs)
class AuthenticatedHandler(RequestHandler):
"""A RequestHandler with an authenticated user."""
def clear_login_cookie(self):
self.clear_cookie(self.cookie_name)
def get_current_user(self):
user_id = self.get_secure_cookie(self.cookie_name)
# For now the user_id should not return empty, but it could eventually
if user_id == '':
user_id = 'anonymous'
if user_id is None:
# prevent extra Invalid cookie sig warnings:
self.clear_login_cookie()
if not self.read_only and not self.login_available:
user_id = 'anonymous'
return user_id
@property
def cookie_name(self):
return self.settings.get('cookie_name', '')
@property
def password(self):
"""our password"""
return self.settings.get('password', '')
@property
def logged_in(self):
"""Is a user currently logged in?
"""
user = self.get_current_user()
return (user and not user == 'anonymous')
@property
def login_available(self):
"""May a user proceed to log in?
This returns True if login capability is available, irrespective of
whether the user is already logged in or not.
"""
return bool(self.settings.get('password', ''))
@property
def read_only(self):
"""Is the notebook read-only?
"""
return self.settings.get('read_only', False)
class IPythonHandler(AuthenticatedHandler):
"""IPython-specific extensions to authenticated handling
Mostly property shortcuts to IPython-specific settings.
"""
@property
def config(self):
return self.settings.get('config', None)
@property
def log(self):
"""use the IPython log by default, falling back on tornado's logger"""
if Application.initialized():
return Application.instance().log
else:
return app_log
@property
def use_less(self):
"""Use less instead of css in templates"""
return self.settings.get('use_less', False)
#---------------------------------------------------------------
# URLs
#---------------------------------------------------------------
@property
def ws_url(self):
"""websocket url matching the current request
turns http[s]://host[:port] into
ws[s]://host[:port]
"""
proto = self.request.protocol.replace('http', 'ws')
host = self.settings.get('websocket_host', '')
# default to config value
if host == '':
host = self.request.host # get from request
return "%s://%s" % (proto, host)
@property
def mathjax_url(self):
return self.settings.get('mathjax_url', '')
@property
def base_project_url(self):
return self.settings.get('base_project_url', '/')
@property
def base_kernel_url(self):
return self.settings.get('base_kernel_url', '/')
#---------------------------------------------------------------
# Manager objects
#---------------------------------------------------------------
@property
def kernel_manager(self):
return self.settings['kernel_manager']
@property
def notebook_manager(self):
return self.settings['notebook_manager']
@property
def cluster_manager(self):
return self.settings['cluster_manager']
@property
def project(self):
return self.notebook_manager.notebook_dir
#---------------------------------------------------------------
# template rendering
#---------------------------------------------------------------
def get_template(self, name):
"""Return the jinja template object for a given name"""
return self.settings['jinja2_env'].get_template(name)
def render_template(self, name, **ns):
ns.update(self.template_namespace)
template = self.get_template(name)
return template.render(**ns)
@property
def template_namespace(self):
return dict(
base_project_url=self.base_project_url,
base_kernel_url=self.base_kernel_url,
read_only=self.read_only,
logged_in=self.logged_in,
login_available=self.login_available,
use_less=self.use_less,
)
class AuthenticatedFileHandler(IPythonHandler, web.StaticFileHandler):
"""static files should only be accessible when logged in"""
@authenticate_unless_readonly
def get(self, path):
return web.StaticFileHandler.get(self, path)
class ProjectDashboardHandler(IPythonHandler):
@authenticate_unless_readonly
def get(self):
self.write(self.render_template('projectdashboard.html',
project=self.project,
project_component=self.project.split('/'),
))
class LoginHandler(IPythonHandler):
def _render(self, message=None):
self.write(self.render_template('login.html',
next=url_escape(self.get_argument('next', default=self.base_project_url)),
message=message,
))
def get(self):
if self.current_user:
self.redirect(self.get_argument('next', default=self.base_project_url))
else:
self._render()
def post(self):
pwd = self.get_argument('password', default=u'')
if self.login_available:
if passwd_check(self.password, pwd):
self.set_secure_cookie(self.cookie_name, str(uuid.uuid4()))
else:
self._render(message={'error': 'Invalid password'})
return
self.redirect(self.get_argument('next', default=self.base_project_url))
class LogoutHandler(IPythonHandler):
def get(self):
self.clear_login_cookie()
if self.login_available:
message = {'info': 'Successfully logged out.'}
else:
message = {'warning': 'Cannot log out. Notebook authentication '
'is disabled.'}
self.write(self.render_template('logout.html',
message=message))
class NewHandler(IPythonHandler):
@web.authenticated
def get(self):
notebook_id = self.notebook_manager.new_notebook()
self.redirect('/' + urljoin(self.base_project_url, notebook_id))
class NamedNotebookHandler(IPythonHandler):
@authenticate_unless_readonly
def get(self, notebook_id):
nbm = self.notebook_manager
if not nbm.notebook_exists(notebook_id):
raise web.HTTPError(404, u'Notebook does not exist: %s' % notebook_id)
self.write(self.render_template('notebook.html',
project=self.project,
notebook_id=notebook_id,
kill_kernel=False,
mathjax_url=self.mathjax_url,
)
)
#-----------------------------------------------------------------------------
# Kernel handlers
#-----------------------------------------------------------------------------
class MainKernelHandler(IPythonHandler):
@web.authenticated
def get(self):
km = self.kernel_manager
self.finish(jsonapi.dumps(km.list_kernel_ids()))
@web.authenticated
def post(self):
km = self.kernel_manager
nbm = self.notebook_manager
notebook_id = self.get_argument('notebook', default=None)
kernel_id = km.start_kernel(notebook_id, cwd=nbm.notebook_dir)
data = {'ws_url':self.ws_url,'kernel_id':kernel_id}
self.set_header('Location', '{0}kernels/{1}'.format(self.base_kernel_url, kernel_id))
self.finish(jsonapi.dumps(data))
class KernelHandler(IPythonHandler):
SUPPORTED_METHODS = ('DELETE')
@web.authenticated
def delete(self, kernel_id):
km = self.kernel_manager
km.shutdown_kernel(kernel_id)
self.set_status(204)
self.finish()
class KernelActionHandler(IPythonHandler):
@web.authenticated
def post(self, kernel_id, action):
km = self.kernel_manager
if action == 'interrupt':
km.interrupt_kernel(kernel_id)
self.set_status(204)
if action == 'restart':
km.restart_kernel(kernel_id)
data = {'ws_url':self.ws_url, 'kernel_id':kernel_id}
self.set_header('Location', '{0}kernels/{1}'.format(self.base_kernel_url, kernel_id))
self.write(jsonapi.dumps(data))
self.finish()
class ZMQStreamHandler(websocket.WebSocketHandler):
def clear_cookie(self, *args, **kwargs):
"""meaningless for websockets"""
pass
def _reserialize_reply(self, msg_list):
"""Reserialize a reply message using JSON.
This takes the msg list from the ZMQ socket, unserializes it using
self.session and then serializes the result using JSON. This method
should be used by self._on_zmq_reply to build messages that can
be sent back to the browser.
"""
idents, msg_list = self.session.feed_identities(msg_list)
msg = self.session.unserialize(msg_list)
try:
msg['header'].pop('date')
except KeyError:
pass
try:
msg['parent_header'].pop('date')
except KeyError:
pass
msg.pop('buffers')
return jsonapi.dumps(msg, default=date_default)
def _on_zmq_reply(self, msg_list):
# Sometimes this gets triggered when the on_close method is scheduled in the
# eventloop but hasn't been called.
if self.stream.closed(): return
try:
msg = self._reserialize_reply(msg_list)
except Exception:
self.log.critical("Malformed message: %r" % msg_list, exc_info=True)
else:
self.write_message(msg)
def allow_draft76(self):
"""Allow draft 76, until browsers such as Safari update to RFC 6455.
This has been disabled by default in tornado in release 2.2.0, and
support will be removed in later versions.
"""
return True
class AuthenticatedZMQStreamHandler(ZMQStreamHandler, IPythonHandler):
def open(self, kernel_id):
self.kernel_id = kernel_id.decode('ascii')
self.session = Session(config=self.config)
self.save_on_message = self.on_message
self.on_message = self.on_first_message
def _inject_cookie_message(self, msg):
"""Inject the first message, which is the document cookie,
for authentication."""
if not PY3 and isinstance(msg, unicode):
# Cookie constructor doesn't accept unicode strings
# under Python 2.x for some reason
msg = msg.encode('utf8', 'replace')
try:
identity, msg = msg.split(':', 1)
self.session.session = identity.decode('ascii')
except Exception:
logging.error("First ws message didn't have the form 'identity:[cookie]' - %r", msg)
try:
self.request._cookies = Cookie.SimpleCookie(msg)
except:
self.log.warn("couldn't parse cookie string: %s",msg, exc_info=True)
def on_first_message(self, msg):
self._inject_cookie_message(msg)
if self.get_current_user() is None:
self.log.warn("Couldn't authenticate WebSocket connection")
raise web.HTTPError(403)
self.on_message = self.save_on_message
class ZMQChannelHandler(AuthenticatedZMQStreamHandler):
@property
def max_msg_size(self):
return self.settings.get('max_msg_size', 65535)
def create_stream(self):
km = self.kernel_manager
meth = getattr(km, 'connect_%s' % self.channel)
self.zmq_stream = meth(self.kernel_id, identity=self.session.bsession)
def initialize(self, *args, **kwargs):
self.zmq_stream = None
def on_first_message(self, msg):
try:
super(ZMQChannelHandler, self).on_first_message(msg)
except web.HTTPError:
self.close()
return
try:
self.create_stream()
except web.HTTPError:
# WebSockets don't response to traditional error codes so we
# close the connection.
if not self.stream.closed():
self.stream.close()
self.close()
else:
self.zmq_stream.on_recv(self._on_zmq_reply)
def on_message(self, msg):
if len(msg) < self.max_msg_size:
msg = jsonapi.loads(msg)
self.session.send(self.zmq_stream, msg)
def on_close(self):
# This method can be called twice, once by self.kernel_died and once
# from the WebSocket close event. If the WebSocket connection is
# closed before the ZMQ streams are setup, they could be None.
if self.zmq_stream is not None and not self.zmq_stream.closed():
self.zmq_stream.on_recv(None)
self.zmq_stream.close()
class IOPubHandler(ZMQChannelHandler):
channel = 'iopub'
def create_stream(self):
super(IOPubHandler, self).create_stream()
km = self.kernel_manager
km.add_restart_callback(self.kernel_id, self.on_kernel_restarted)
km.add_restart_callback(self.kernel_id, self.on_restart_failed, 'dead')
def on_close(self):
km = self.kernel_manager
if self.kernel_id in km:
km.remove_restart_callback(
self.kernel_id, self.on_kernel_restarted,
)
km.remove_restart_callback(
self.kernel_id, self.on_restart_failed, 'dead',
)
super(IOPubHandler, self).on_close()
def _send_status_message(self, status):
msg = self.session.msg("status",
{'execution_state': status}
)
self.write_message(jsonapi.dumps(msg, default=date_default))
def on_kernel_restarted(self):
logging.warn("kernel %s restarted", self.kernel_id)
self._send_status_message('restarting')
def on_restart_failed(self):
logging.error("kernel %s restarted failed!", self.kernel_id)
self._send_status_message('dead')
def on_message(self, msg):
"""IOPub messages make no sense"""
pass
class ShellHandler(ZMQChannelHandler):
channel = 'shell'
class StdinHandler(ZMQChannelHandler):
channel = 'stdin'
#-----------------------------------------------------------------------------
# Notebook web service handlers
#-----------------------------------------------------------------------------
class NotebookRedirectHandler(IPythonHandler):
@authenticate_unless_readonly
def get(self, notebook_name):
# strip trailing .ipynb:
notebook_name = os.path.splitext(notebook_name)[0]
notebook_id = self.notebook_manager.rev_mapping.get(notebook_name, '')
if notebook_id:
url = self.settings.get('base_project_url', '/') + notebook_id
return self.redirect(url)
else:
raise HTTPError(404)
class NotebookRootHandler(IPythonHandler):
@authenticate_unless_readonly
def get(self):
nbm = self.notebook_manager
km = self.kernel_manager
files = nbm.list_notebooks()
for f in files :
f['kernel_id'] = km.kernel_for_notebook(f['notebook_id'])
self.finish(jsonapi.dumps(files))
@web.authenticated
def post(self):
nbm = self.notebook_manager
body = self.request.body.strip()
format = self.get_argument('format', default='json')
name = self.get_argument('name', default=None)
if body:
notebook_id = nbm.save_new_notebook(body, name=name, format=format)
else:
notebook_id = nbm.new_notebook()
self.set_header('Location', '{0}notebooks/{1}'.format(self.base_project_url, notebook_id))
self.finish(jsonapi.dumps(notebook_id))
class NotebookHandler(IPythonHandler):
SUPPORTED_METHODS = ('GET', 'PUT', 'DELETE')
@authenticate_unless_readonly
def get(self, notebook_id):
nbm = self.notebook_manager
format = self.get_argument('format', default='json')
last_mod, name, data = nbm.get_notebook(notebook_id, format)
if format == u'json':
self.set_header('Content-Type', 'application/json')
self.set_header('Content-Disposition','attachment; filename="%s.ipynb"' % name)
elif format == u'py':
self.set_header('Content-Type', 'application/x-python')
self.set_header('Content-Disposition','attachment; filename="%s.py"' % name)
self.set_header('Last-Modified', last_mod)
self.finish(data)
@web.authenticated
def put(self, notebook_id):
nbm = self.notebook_manager
format = self.get_argument('format', default='json')
name = self.get_argument('name', default=None)
nbm.save_notebook(notebook_id, self.request.body, name=name, format=format)
self.set_status(204)
self.finish()
@web.authenticated
def delete(self, notebook_id):
self.notebook_manager.delete_notebook(notebook_id)
self.set_status(204)
self.finish()
class NotebookCheckpointsHandler(IPythonHandler):
SUPPORTED_METHODS = ('GET', 'POST')
@web.authenticated
def get(self, notebook_id):
"""get lists checkpoints for a notebook"""
nbm = self.notebook_manager
checkpoints = nbm.list_checkpoints(notebook_id)
data = jsonapi.dumps(checkpoints, default=date_default)
self.finish(data)
@web.authenticated
def post(self, notebook_id):
"""post creates a new checkpoint"""
nbm = self.notebook_manager
checkpoint = nbm.create_checkpoint(notebook_id)
data = jsonapi.dumps(checkpoint, default=date_default)
self.set_header('Location', '{0}notebooks/{1}/checkpoints/{2}'.format(
self.base_project_url, notebook_id, checkpoint['checkpoint_id']
))
self.finish(data)
class ModifyNotebookCheckpointsHandler(IPythonHandler):
SUPPORTED_METHODS = ('POST', 'DELETE')
@web.authenticated
def post(self, notebook_id, checkpoint_id):
"""post restores a notebook from a checkpoint"""
nbm = self.notebook_manager
nbm.restore_checkpoint(notebook_id, checkpoint_id)
self.set_status(204)
self.finish()
@web.authenticated
def delete(self, notebook_id, checkpoint_id):
"""delete clears a checkpoint for a given notebook"""
nbm = self.notebook_manager
nbm.delte_checkpoint(notebook_id, checkpoint_id)
self.set_status(204)
self.finish()
class NotebookCopyHandler(IPythonHandler):
@web.authenticated
def get(self, notebook_id):
notebook_id = self.notebook_manager.copy_notebook(notebook_id)
self.redirect('/'+urljoin(self.base_project_url, notebook_id))
#-----------------------------------------------------------------------------
# Cluster handlers
#-----------------------------------------------------------------------------
class MainClusterHandler(IPythonHandler):
@web.authenticated
def get(self):
self.finish(jsonapi.dumps(self.cluster_manager.list_profiles()))
class ClusterProfileHandler(IPythonHandler):
@web.authenticated
def get(self, profile):
self.finish(jsonapi.dumps(self.cluster_manager.profile_info(profile)))
class ClusterActionHandler(IPythonHandler):
@web.authenticated
def post(self, profile, action):
cm = self.cluster_manager
if action == 'start':
n = self.get_argument('n',default=None)
if n is None:
data = cm.start_cluster(profile)
else:
data = cm.start_cluster(profile, int(n))
if action == 'stop':
data = cm.stop_cluster(profile)
self.finish(jsonapi.dumps(data))
#-----------------------------------------------------------------------------
# File handler
#-----------------------------------------------------------------------------
# to minimize subclass changes:
HTTPError = web.HTTPError
class FileFindHandler(web.StaticFileHandler):
"""subclass of StaticFileHandler for serving files from a search path"""
_static_paths = {}
# _lock is needed for tornado < 2.2.0 compat
_lock = threading.Lock() # protects _static_hashes
def initialize(self, path, default_filename=None):
if isinstance(path, basestring):
path = [path]
self.roots = tuple(
os.path.abspath(os.path.expanduser(p)) + os.path.sep for p in path
)
self.default_filename = default_filename
@classmethod
def locate_file(cls, path, roots):
"""locate a file to serve on our static file search path"""
with cls._lock:
if path in cls._static_paths:
return cls._static_paths[path]
try:
abspath = os.path.abspath(filefind(path, roots))
except IOError:
# empty string should always give exists=False
return ''
# os.path.abspath strips a trailing /
# it needs to be temporarily added back for requests to root/
if not (abspath + os.path.sep).startswith(roots):
raise HTTPError(403, "%s is not in root static directory", path)
cls._static_paths[path] = abspath
return abspath
def get(self, path, include_body=True):
path = self.parse_url_path(path)
# begin subclass override
abspath = self.locate_file(path, self.roots)
# end subclass override
if os.path.isdir(abspath) and self.default_filename is not None:
# need to look at the request.path here for when path is empty
# but there is some prefix to the path that was already
# trimmed by the routing
if not self.request.path.endswith("/"):
self.redirect(self.request.path + "/")
return
abspath = os.path.join(abspath, self.default_filename)
if not os.path.exists(abspath):
raise HTTPError(404)
if not os.path.isfile(abspath):
raise HTTPError(403, "%s is not a file", path)
stat_result = os.stat(abspath)
modified = datetime.datetime.utcfromtimestamp(stat_result[stat.ST_MTIME])
self.set_header("Last-Modified", modified)
mime_type, encoding = mimetypes.guess_type(abspath)
if mime_type:
self.set_header("Content-Type", mime_type)
cache_time = self.get_cache_time(path, modified, mime_type)
if cache_time > 0:
self.set_header("Expires", datetime.datetime.utcnow() + \
datetime.timedelta(seconds=cache_time))
self.set_header("Cache-Control", "max-age=" + str(cache_time))
else:
self.set_header("Cache-Control", "public")
self.set_extra_headers(path)
# Check the If-Modified-Since, and don't send the result if the
# content has not been modified
ims_value = self.request.headers.get("If-Modified-Since")
if ims_value is not None:
date_tuple = email.utils.parsedate(ims_value)
if_since = datetime.datetime(*date_tuple[:6])
if if_since >= modified:
self.set_status(304)
return
with open(abspath, "rb") as file:
data = file.read()
hasher = hashlib.sha1()
hasher.update(data)
self.set_header("Etag", '"%s"' % hasher.hexdigest())
if include_body:
self.write(data)
else:
assert self.request.method == "HEAD"
self.set_header("Content-Length", len(data))
@classmethod
def get_version(cls, settings, path):
"""Generate the version string to be used in static URLs.
This method may be overridden in subclasses (but note that it
is a class method rather than a static method). The default
implementation uses a hash of the file's contents.
``settings`` is the `Application.settings` dictionary and ``path``
is the relative location of the requested asset on the filesystem.
The returned value should be a string, or ``None`` if no version
could be determined.
"""
# begin subclass override:
static_paths = settings['static_path']
if isinstance(static_paths, basestring):
static_paths = [static_paths]
roots = tuple(
os.path.abspath(os.path.expanduser(p)) + os.path.sep for p in static_paths
)
try:
abs_path = filefind(path, roots)
except IOError:
app_log.error("Could not find static file %r", path)
return None
# end subclass override
with cls._lock:
hashes = cls._static_hashes
if abs_path not in hashes:
try:
f = open(abs_path, "rb")
hashes[abs_path] = hashlib.md5(f.read()).hexdigest()
f.close()
except Exception:
app_log.error("Could not open static file %r", path)
hashes[abs_path] = None
hsh = hashes.get(abs_path)
if hsh:
return hsh[:5]
return None
def parse_url_path(self, url_path):
"""Converts a static URL path into a filesystem path.
``url_path`` is the path component of the URL with
``static_url_prefix`` removed. The return value should be
filesystem path relative to ``static_path``.
"""
if os.path.sep != "/":
url_path = url_path.replace("/", os.path.sep)
return url_path