A brief example outlining some locale problems on OS X with Python 3.0
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While helping Brandon Rhodes to port PyEphem[1] to Python 3 we struggled over a
strange locale-related problem on OS X. PyEphem is a library which can do
astronomical computations like tracking the position of stars, planets and
earth satellites relative to the earth's position. When testing out the Python
3 release of PyEphem I noticed that on my OS X laptop a lot of calculations
were wrong (not completely wrong, but clearly not accurate) compared to Python
2.5. We (well mostly Brandon) were able to track down the problem to the TLE
parser (TLE are data file containing the orbital elements of an object) which
appears to read most values wrong with python 3. In fact it cut of the decimal
parts of all floats (1.123232 got 1, etc). Manually setting LANG and LC_ALL to
C solved the problem. 

It turns out that some parts of Python 3 got more locale dependent on some
platforms. The only platform I am aware of is OS X, on Linux Python 3 appears
to behave like Python 2.x did. 

In case of PyEphem the problem was in the C extension which got more locale
dependent, for example atof() or scanf() with Python 3 now expected the german
decimal-delimiter ',' instead of the '.' in floats (3.14 vs. 3,14). On the
other hand the constructor of float still expects '.' all the time. But the
built-in function strptime() honors locales with Python 3 and expects german
week day.

I've written a simple script and a simple C extension which illustrates the
problem. Both the extension and the script run python 2.x and python 3, so you
can easily compare the result while executing the script in different

I was only able to reproduce the problem on OS X (10.5) and using a german
locale like "de_CH.UTF-8". When manually setting LC_ALL=C, the differences

I can't imagine that his behavior was really intended, and I hope the test case
helps you guys to identify/fix this problem.

Download the test case from: 
or get it using git:

You can use the following steps to build it:

$ python2.5 setup.py build
$ python3.0 setup.py build

To run the tests with python 2.5, enter:
$ (cd build/lib*-2.5; python2.5 py3k_locale_problem.py)
... for 3.0  ... 
$ (cd build/lib*-3.0; python3.0 py3k_locale_problem.py)

In the file 'results.txt' you can see the output from my OS X system. 

Reto Schüttel

[1] http://rhodesmill.org/pyephem/