If one line of a CSV file is missing one or more
commas, the delimiter detection code of the Sniffer
class fails, setting delimiter to an empty string.

This leads to a totally misleading error when using
has_header(). 

This code shows the problem (Python 2.4.2, FC3 and
Ubuntu Breezy):

import csv

str1 = "a,b,c,d\r\n1,2,foo bar,dead
beef\r\nthis,line,is,ok\r\n"
str2 = "a,b,c,d\r\n1,2,foo bar,dead beef\r\nthis,line
is,not\r\n"

s = csv.Sniffer()

d1 = s.sniff(str1)
d2 = s.sniff(str2)

for line in str1.split('\r\n'):
    print line.count(',')

print d1.delimiter
print s.has_header(str1)

for line in str2.split('\r\n'):
    print line.count(',')

print d2.delimiter
print s.has_header(str2)

Problem is still there as of Python 2.4.3.

Trying to read in a file whose lines have a different number of fields, I get:

Traceback (most recent call last):
  File "../myscript.py", line 59, in ?
    main()
  File "../myscript.py", line 30, in main
    reader = csv.reader(fin, dialect)
TypeError: bad argument type for built-in operation

where "dialect" has been sniffed by feeding the first two lines to the Sniffer.

What I expect is to either:
  1. get different sized rows, with no exception raised
  2. get a csv.Error instead of the TypeError above

Thanks

This appears to work better in 2.5 and 2.6 (it doesn't crash, though it 
gets the delimiter wrong) but does indeed fail in 2.4.

Closing as won't fix.  There are bound to be limits to how the Sniffer
class works.  I'm not sure it's worth the effort necessary to fix this
corner case.

(Andrew, reopen if you want to tackle this.)