Convert a filename to a file:// URL

Question

In WeasyPrint’s public API I accept filenames (among other types) for the HTML inputs. Any filename that works with the built-in open() should work, but I need to convert it to an URL in the file:// scheme that will later be passed to urllib.urlopen().

(Everything is in URL form internally. I need to have a "base URL" for documents in order to resolve relative URL references with urlparse.urljoin().)

urllib.pathname2url is a start:

Convert the pathname path from the local syntax for a path to the form used in the path component of a URL. This does not produce a complete URL. The return value will already be quoted using the quote() function.

The emphasis is mine, but I do need a complete URL. So far this seems to work:

def path2url(path):
    """Return file:// URL from a filename."""
    path = os.path.abspath(path)
    if isinstance(path, unicode):
        path = path.encode('utf8')
    return 'file:' + urlparse.pathname2url(path)

UTF-8 seems to be recommended by RFC 3987 (IRI). But in this case (the URL is meant for urllib, eventually) maybe I should use sys.getfilesystemencoding()?

However, based on the literature I should prepend not just file: but file:// ... except when I should not: On Windows the results from nturl2path.pathname2url() already start with three slashes.

So the question is: is there a better way to do this and make it cross-platform?

Vaishnava

Couldn't you just check for something like url[0:2] == '///', and if false add the two extra slashes? – Microclimatology

Joachim, maybe that would work. I just don’t know what rules to follow to avoid surprising corner-cases. – Vaishnava

Hey, your example code uses urlparse.pathname2url, which doesn't exist. Did you mean urllib.pathname2url? – Extravasation

Answer 1

For completeness, in Python 3.4+, you should do:

import pathlib

pathlib.Path(absolute_path_string).as_uri()

Manis

This module is also on PyPI (for other Python versions) pypi.python.org/pypi/pathlib – Vaishnava

pathlib2 should now be used for other Python versions – Lumper

as_uri() doesn't work on relative filenames (there are use cases for converting only partial filename to (partial) URL – Soprano

Relative URLs can be easily supported using pathlibs resolve() function, e.g. pathlib.Path(src).resolve().as_uri() – Yasmineyasu

Answer 2

I'm not sure the docs are rigorous enough to guarantee it, but I think this works in practice:

import urlparse, urllib

def path2url(path):
    return urlparse.urljoin(
      'file:', urllib.pathname2url(path))

Pinero

Tested on Linux, Windows, and OS X and it works fine on all three. – Incept

And in py3k this becomes import urlib.parse as urlparse and import urlib.request as urllib – Larentia

you should probably call os.path.abspath(path) here. – Faucal

If you use the six library to assure Python 2 and 3 portability: return six.moves.urllib_parse.urljoin( "file://", six.moves.urllib.request.pathname2url(path)) – Numerical

This produces urls that look like file:///C:/foo%20bar/spam/eggs" Shouldn't it be file:///C%3A/foo%20bar/spam/eggs" with the colon turned into %3A? – Tiepolo

@stib: aparently not, not on Windows, where the drive letter colon is to be kept intact. See blogs.msdn.microsoft.com/ie/2006/12/06/file-uris-in-windows and en.wikipedia.org/wiki/File_URI_scheme#Windows_2 – Clingy

Answer 3

Credit to comment from @danodonovan above.

For Python3, the following code will work:

from urllib.parse import urljoin
from urllib.request import pathname2url

def path2url(path):
    return urljoin('file:', pathname2url(path))

Hoo

Answer 4

Does the following work for you?

from urlparse import urlparse, urlunparse

urlunparse(urlparse('yourURL')._replace(scheme='file'))

Sarasvati

The idea is interesting, but I don’t know if this is enough. In particular, ` in Windows filenames is supposed to become /. Still on Windows, The C in C:\foo\bar.html` is parsed as a scheme and then replaced. The expected output would be file:///C:/foo/bar.html. – Vaishnava