[Python-Dev] teaching the new urllib (original) (raw)

Tres Seaver tseaver at palladion.com
Wed Feb 4 00:50:44 CET 2009

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Brett Cannon wrote:

On Tue, Feb 3, 2009 at 11:08, Brad Miller <millbr02 at luther.edu> wrote:

I'm just getting ready to start the semester using my new book (Python Programming in Context) and noticed that I somehow missed all the changes to urllib in python 3.0. ARGH to say the least. I like using urllib in the intro class because we can get data from places that are more interesting/motivating/relevant to the students. Here are some of my observations on trying to do very basic stuff with urllib: 1. urllib.urlopen is now urllib.request.urlopen Technically urllib2.urlopen became urllib.request.urlopen. See PEP 3108 for the details of the reorganization.

2. The object returned by urlopen is no longer iterable! no more for line in url. That is probably a difference between urllib2 and urllib. 3. read, readline, readlines now return bytes objects or arrays of bytes instead of a str and array of str Correct. 4. Taking the naive approach to converting a bytes object to a str does not work as you would expect.

import urllib.request page = urllib.request.urlopen('http://knuth.luther.edu/test.html') page <addinfourl at 16419792 whose fp = <socket.SocketIO object at 0xfa8570>> line = page.readline() line b'<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"\n' str(line) 'b'<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"\n'' As you can see from the example the 'b' becomes part of the string! It seems like this should be a bug, is it? No because you are getting back the repr for the bytes object. Str does not know what the encoding is for the bytes so it has no way of performing the decoding.

The encoding information is available in the response headers, e.g.:

Resolving knuth.luther.edu... 192.203.196.71 Connecting to knuth.luther.edu|192.203.196.71|:80... connected. HTTP request sent, awaiting response... HTTP/1.1 200 OK Date: Tue, 03 Feb 2009 23:46:28 GMT Server: Apache/2.0.50 (Linux/SUSE) Last-Modified: Mon, 17 Sep 2007 23:35:49 GMT ETag: "2fcd8-1d8-43b2bf40" Accept-Ranges: bytes Content-Length: 472 Keep-Alive: timeout=15, max=100 Connection: Keep-Alive Content-Type: text/html; charset=ISO-8859-1 Length: 472 [text/html] 200 OK

So, the OP's use case could be satisfied, assuming that the Py3K version of urllib sprouted a means of leveraging that header. In this sense, fetching the resource over HTTP is better than loading it from a file: information about the character set is explicit, and highly likely to be correct, at least for any resource people expect to render cleanly in a browser.

Tres. - --

Tres Seaver +1 540-429-0999 tseaver at palladion.com Palladion Software "Excellence by Design" http://palladion.com -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

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