Feature Requests item #1437699, was opened at 2006-02-23 21:07
Message generated for change (Comment added) made by gbrandl
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>Category: Unicode
>Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: osvenskan (osvenskan)
Assigned to: M.-A. Lemburg (lemburg)
>Summary: allow unicode arguments for robotparser.can_fetch
Initial Comment:
One-line summary: If the robotparser module encounters
a robots.txt file that contains non-ASCII characters
AND I pass a Unicode user agent string to can_fetch(),
that function crashes with a TypeError under Python
2.4. Under Python 2.3, the error is a UnicodeDecodeError.
More detail:
When one calls can_fetch(MyUserAgent, url), the
robotparser module compares the UserAgent to each user
agent described in the robots.txt file. If
isinstance(MyUserAgent, str) == True then the
comparison does not raise an error regardless of the
contents of robots.txt. However, if
isinstance(MyUserAgent, unicode) == True, then Python
implicitly tries to convert the contents of the
robots.txt file to Unicode before comparing it to
MyUserAgent. By default, Python assumes a US-ASCII
encoding when converting, so if the contents of
robots.txt aren't ASCII, the conversion fails. In other
words, this works:
MyRobotParser.can_fetch('foobot', url)
but this fails:
MyRobotParser.can_fetch(u'foobot', url)
I recreated this with Python 2.4.1 on FreeBSD 6 and
Python 2.3 under Darwin/OS X. I'll attach examples from
both. The URLs that I use in the attachments are from
my Web site and will remain live. They reference
robots.txt files which contain an umlaut-ed 'a' (0xe4
in iso-8859-1). They're served up using a special
.htaccess file that adds a Content-Type header which
correctly identifies the encoding used for each file.
Here's the contents of the .htaccess file:
AddCharset iso-8859-1 .iso8859-1
AddCharset utf-8 .utf8
A suggested solution:
AFAICT, the construction of robots.txt is still defined
by "a consensus on 30 June 1994 on the robots mailing
list" [http://www.robotstxt.org/wc/norobots.html] and a
1996 draft proposal
[http://www.robotstxt.org/wc/norobots-rfc.html] that
has never evolved into a formal standard. Neither of
these mention character sets or encodings which is no
surprise considering that they date back to the days
when the Internet was poor but happy and we considered
even ASCII a luxury and we were grateful to have it.
("ASCII? We used to dream of having ASCII. We only had
one bit, and it was a zero. We lived in a shoebox in
the middle of the road..." etc.) A backwards-compatible
yet forward-looking solution would be to have the
robotparser module respect the Content-Type header sent
with robots.txt. If no such header is present,
robotparser should try to decode it using iso-8859-1
per section 3.7.1 of the HTTP 1.1 spec
(http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.7.1)
which says, 'When no explicit charset parameter is
provided by the sender, media subtypes of the "text"
type are defined to have a default charset value of
"ISO-8859-1" when received via HTTP. Data in character
sets other than "ISO-8859-1" or its subsets MUST be
labeled with an appropriate charset value.' Section
3.6.1 of the HTTP 1.0 spec says the same. Since
ISO-8859-1 is a superset of US-ASCII, robots.txt files
that are pure ASCII won't be affected by the change.
----------------------------------------------------------------------
>Comment By: Georg Brandl (gbrandl)
Date: 2006-03-18 10:17
Message:
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Turning into a Feature Request.
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Comment By: osvenskan (osvenskan)
Date: 2006-03-07 16:32
Message:
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Thanks for looking at this. I have some followup comments.
The list at robotstxt.org is many years stale (note that
Google's bot is present only as Backrub which was still a
server at Stanford at the time:
http://www.robotstxt.org/wc/active/html/backrub.html) but
nevertheless AFAICT it is the most current bot list on the
Web. If you look carefully, the list *does* contain a
non-ASCII entry (#76 --easy to miss in that long list). That
Finnish bot is gone but it has left a legacy in the form of
many robots.txt files that were created by automated tools
based on the robotstxt.org list. Google helps us here:
http://www.google.com/search?q=allintext%3AH%C3%A4m%C3%A4h%C3%A4kki+disallow+filetype%3Atxt
And by Googling for some common non-ASCII words and letters
I can find more like this one (look at the end of the
alphabetical list):
http://paranormal.se/robots.txt
Robots.txt files that contain non-ASCII are few and far
between, it seems, but they're out there.
Which leads me to a nitpicky (but important!) point about
Unicode. As you point out, the spec doesn't mention Unicode;
it says nothing at all on the topic of encodings. My
argument is that just because the spec doesn't mention
encodings doesn't let us off the hook because the HTTP
1.0/1.1 specs are very clear that iso-8859-1, not US-ASCII,
is the default for text content delivered via HTTP. By my
interpretation, this means that the robots.txt examples
provided above are compliant with published specs, therefore
code that fails to interpret them does not comply. There's
no obvious need for robotparser to support full-blown
Unicode, just iso-8859-1.
You might be interested in a replacement for this module
that I've implemented. It does everything that robotparser
does and also handles non-ASCII plus a few other things. It
is GPL; you're welcome to copy it in part or lock, stock and
barrel. So far I've only tested it "in the lab" but I've
done fairly extensive unit testing and I'll soon be testing
it on real-world data. The code and docs are here:
http://semanchuk.com/philip/boneyard/rerp/
Comments & feedback would be most welcome.
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Comment By: Terry J. Reedy (tjreedy)
Date: 2006-03-06 03:01
Message:
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To me, this is not a bug report but at best an RFE. The
reported behavior is what I would expect. I read both
module doc and the referenced web page and further links.
The doc does not mention Unicode as allowed and the 300
registered UserAgents at
http://www.robotstxt.org/wc/active/html/index.html
all have ascii names.
So I recomment closing this as a bug report but will give
ML a chance to respond. If switched instead to Feature
Request, I would think it would need some 'in the wild'
evidence of need.
----------------------------------------------------------------------
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