I have a list of floats read in from a text file. After some data processing I write the list to a file using:
for val in flist:
sa = '{0}'.format(val)
fout.write(sa)
For specific input files, the output file will have a ':' in the string. I have run debug and stopped the script at the point of failure. The value should be 58710000.0
[Dbg]>>> print val[464]
5870:000.0
[Dbg]>>> fa = val[464]
[Dbg]>>> print fa
5870:000.0
[Dbg]>>>
[Dbg]>>> fa = fa + 1
[Dbg]>>> print fa
58710001.0
[Dbg]>>> fa = fa - 1
[Dbg]>>> print fa
5870:000.0
This happens only for certain files and floats
Any suggestions?
It's a bug in Python 2.7.3 or perhaps earlier, with certain environments.
User @ecatmur pointed out in a different post with a similar question, that '9' + 1 = ':' in ASCII
This has been Fixed in later versions of Python.
Specifically, the problem disappeared in Python 2.7.5 so the issue has been fixed.
See Gord Thompson's accepted answer on:
Similar questions were closed or not answered:
Your values are probably not actually floats. Anyhow, sa = '{0}'.format(val) is silly; you might as well do just sa = str(val). But if you do sa = '%f' % (val,) instead, you will get an exception when val is not a float.
This appears to be highly platform specific. The repr for float calls PyOS_double_to_string which ends up calling PyOS_snprintf, which wraps snprintf with some code to make that function more consistent across platforms. It appears on some version of AIX in particular, snprintf can produce 0: instead of 10.
Could you share your sys.platform and sys.version values? (The version header printed when you start an interactive python interpreter should do.)
Relevant source files: Python/mysnprintf.c for PyOS_snprintf, Objects/floatobject.c for float_repr, Python/pystrtod.c for PyOS_string_to_double.
来源：https://stackoverflow.com/questions/14226486/python-list-of-floats-ends-up-with-a-when-converting-to-a-string