Ordering of urlencoded tuples incorrect

benlucas99 at googlemail.com benlucas99 at googlemail.com
Fri Jan 16 11:57:18 CET 2009

On Jan 16, 1:44 am, John Machin <sjmac... at lexicon.net> wrote:
> On Jan 16, 11:59 am, benluca... at googlemail.com wrote:
> > I'm having problems with the ordering of the tuples produced by
> > urllib.urlencode.  Taking an example straight from the docs and so
> > doing the following:
> What are "the docs" you are reading that include such an example? The
> docs distributed with Python 2.5.1 fromwww.python.orghave only this:
> """
> urlencode( query[, doseq])
> Convert a mapping object or a sequence of two-element tuples to a
> ``url-encoded'' string, suitable to pass to urlopen() above as the
> optional data argument. This is useful to pass a dictionary of form
> fields to a POST request. The resulting string is a series of
> key=value pairs separated by "&" characters, where both key and value
> are quoted using quote_plus() above. If the optional parameter doseq
> is present and evaluates to true, individual key=value pairs are
> generated for each element of the sequence. When a sequence of two-
> element tuples is used as the query argument, the first element of
> each tuple is a key and the second is a value. The order of parameters
> in the encoded string will match the order of parameter tuples in the
> sequence. The cgi module provides the functions parse_qs() and
> parse_qsl() which are used to parse query strings into Python data
> structures.
> """
> >         import urllib
> >         ...
> >         params = urllib.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
> >         print params
> > The documentation for urlencode( query[, doseq]) says: "The order of
> > parameters in the encoded string will match the order of parameter
> > tuples in the sequence" but I'm getting:
> "query" can be either a mapping object (e.g. a dictionary, as you have
> used) or a sequence of 2-tuples. No such guarantee as you quote above
> can be made for a mapping; mappings are just not orderable.
> If you want order, give it a sequence, like this:
> | >>> import urllib
> | >>> urllib.urlencode((('spam', 1), ('eggs', 2), ('bacon', 0)))
> | 'spam=1&eggs=2&bacon=0'
> HTH,
> John

Thanks guys, the explanations really helped. I knew I was missing
something fundamental.

The docs I'm referring is section "18.7.3 Examples" in the Python
Library Reference, 18th April, 2007, Release 2.5.1  But looking at it
now I guess the server side procsssing that post request may not care
about ordering (unlike the web API I'm trying to call).


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