Python simplejson coordinates issue

Question

The issue is that in my laptop i have the python 2.7.5 with some version of Simplejson and on my Debian 6 Server I have Python 2.6.6 with some simplejson version .. but whats happening on the debian server is that simplejson is adding extra precision to the coordinates value --

>>> import simplejson as json
>>> streamer_data = json.loads('{"text": "test","geo": {"type": "Point","coordinates":  [52.68908263, -8.50845340]},"coordinates": {"type": "Point","coordinates": [-8.50845340, 52.68908263]}}');

>>> print streamer_data
{u'text': test', u'geo': {u'type': u'Point', u'coordinates': [52.689082630000001, -8.5084534000000005]}, u'id': 420024061457346560L, u'coordinates': {u'type': u'Point', u'coordinates': [-8.5084534000000005, 52.689082630000001]}}

On my laptop this gives the correct result with proper precision to coordinates values --

>>> print streamer_data
{'text': 'test', 'geo': {'type': 'Point', 'coordinates': [52.68908263, -8.5084534]}, 'coordinates': {'type': 'Point', 'coordinates': [-8.5084534, 52.68908263]}}

Is this the Simplejson versioning problem or something else. Also note that i tried to figure out the version of simplejson on debian server but no success.

Hm not sure about that. This may be helpful but it's not simplejson: http://stackoverflow.com/questions/1447287/format-floats-with-standard-json-module — valheru, Jan 06 '14 at 04:09

score 4 · Accepted Answer · answered Jan 06 '14 at 04:42

4

This difference between Python 2.6 and 2.7 has nothing to do with simplejson. In 2.7 there are changes to the algorithms used to produce the string representation and rounding of floating point numbers.

$ python2.6 -c "print([52.68908263, -8.50845340])"
[52.689082630000001, -8.5084534000000005]
$ python2.7 -c "print([52.68908263, -8.50845340])"
[52.68908263, -8.5084534]

answered Jan 06 '14 at 04:42

Ned Deily

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Perfect ..thanks .. this works for me .. the tricky part was to install Python 2.7 on Debian 6 but that issue got resolved by http://www.yodi.sg/install-python-2-7-debian-6-0-squeeze/ – UberNeo Jan 06 '14 at 22:52
BTW any workaround to make this work in Python 2.6 , tried to use this http://stackoverflow.com/a/1447562/2374316 .. but this also doesnt seems to work on 2.6 – UberNeo Jan 09 '14 at 00:08
Do you really need to change this? As Robert Siemer notes in his answer, this is really just a visual difference. The binary values of either the 2.6 or 2.7 representations should be the same. Otherwise, it would probably be simpler to upgrade to Python 2.7. – Ned Deily Jan 09 '14 at 00:12
I am facing problems in upgrading to python 2.7 on Debian .. i have to save these values in a file and there it is showing [52.689082630000001, -8.5084534000000005] – UberNeo Jan 09 '14 at 00:17

score 0 · Answer 2 · answered Jan 06 '14 at 11:05

@Ned’s answer is correct, but I would like to add:

Your issue is only a visual one, both representations are exactly the same on a “normal” computer. Both are also not exactly of what the computer (can) store:

>>> a = 52.68908263
>>> b = 52.689082630000001
>>> '{0:.30} = {1:.30}: {2}'.format(a, b, a==b)
Python 2.6:
'52.6890826300000014725810615346 = 52.6890826300000014725810615346: True'
Python 2.7:
'52.6890826300000014725810615346 = 52.6890826300000014725810615346: True'

As visible now: no difference at all between those numbers. Python2.7 prints shorter representation of numbers, when it can make sure they round back to the same internal value. Python2.7 can do this only on some systems (with some compilers) (check sys.float_repr_style, it is “short” or “legacy”).

Python simplejson coordinates issue

2 Answers2