Unhelpful error message from cgi module

[mdcowles]

BPO	834840
Nosy	@akuchling, @orsenthil, @devdanzin, @ezio-melotti, @merwok

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2013-11-06.20:22:48.842>
created_at = <Date 2003-11-03.02:54:39.000>
labels = ['easy', 'type-bug', 'library']
title = 'Unhelpful error message from cgi module'
updated_at = <Date 2013-11-06.20:22:48.841>
user = 'https://bugs.python.org/mdcowles'

bugs.python.org fields:

activity = <Date 2013-11-06.20:22:48.841>
actor = 'akuchling'
assignee = 'none'
closed = True
closed_date = <Date 2013-11-06.20:22:48.842>
closer = 'akuchling'
components = ['Library (Lib)']
creation = <Date 2003-11-03.02:54:39.000>
creator = 'mdcowles'
dependencies = []
files = []
hgrepos = []
issue_num = 834840
keywords = ['easy']
message_count = 3.0
messages = ['60415', '109263', '114294']
nosy_count = 6.0
nosy_names = ['akuchling', 'mdcowles', 'orsenthil', 'ajaksu2', 'ezio.melotti', 'eric.araujo']
pr_nums = []
priority = 'low'
resolution = 'wont fix'
stage = 'test needed'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue834840'
versions = ['Python 2.7']

[mdcowles]

[From a post to python-help]

If an instance of the cgi module's FieldStorage class doesn't
recognize the HTTP request it's trying to parse as a form, no
error is raised but attempting to access any of the form data
later raises the unhelpful exception TypeError, "not
indexable".

It seems that even Andrew Kuchling was once confused by
this behavior:

http://groups.yahoo.com/group/web-sig/message/28

It happens because in the FieldStorage class's __init__(), the
request's content-type is tested against "multipart/" and
"application/x-www-form-urlencoded". If it doesn't match
either of those, read_single() is called. In that case, self.list
isn't changed from its default of None. That causes any call
to __getitem__() to raise TypeError, "not indexable".

I'm no CGI expert, but I don't see the value of
read_single(). As far as I can tell, it would make sense to
raise TypeError (or perhaps ValueError) at that point with a
message something like, "Data not recognized as a form".

[BreamoreBoy]

Could a CGI expert pick this up, failing that why not simply close it as opened nearely 7 years ago.

[BreamoreBoy]

Closed as no reply to msg109263.