Why can "%.10f" % Decimal(u) emit a string with a literal colon?

Question

When formatting a number to be printed, 12 digit numbers are being formatted with a colon immediately after the dot. Why is this happening? This is Python 2.7 on an AIX system.

$ uname -a ; /opt/bin/python2.7
AIX myserver 1 6 00F6A5CC4C00
Python 2.7.12 (default, Sep 29 2016, 12:02:17) [C] on aix5
Type "help", "copyright", "credits" or "license" for more information.
>>> '{0:.10f}'.format(123456789012)
'123456789011.:000000000'
>>> from decimal import Decimal
>>> u=123456789012
>>> print "%.10f" % Decimal(u)
123456789011.:000000000

Further information:

It is not every 12 digit number:

>>> for x in range(123456789010,123456789020):
...     print '{0:.10f}'.format(x)
...
12345678900:.0000000000
123456789010.:000000000
123456789011.:000000000
123456789013.0000000000
123456789013.:000000000
123456789015.0000000000
123456789016.0000000000
123456789017.0000000000
123456789017.:000000000
123456789019.0000000000

This is not happening with any other length numbers. Also, I tried bash's and perl's printf and this is not happening with either of them.

What is happening here?

As requested, here is a screen shot video.

More requested information:

>>> import locale
>>> locale.getdefaultlocale()
('en_US', 'ISO8859-1')

Result of user2357112 pastebin code:

>>> import ctypes
>>> f=ctypes.pythonapi.PyOS_double_to_string
>>> f.argtypes=ctypes.c_double,ctypes.c_char,ctypes.c_int,ctypes.c_int,ctypes.POINTER(ctypes.c_int))
>>> f.restype=ctypes.c_char_p
>>> print f(123456789012.0, 'f', 10, 0, None)
123456789011.:000000000

Antti_Happa's pastebin printed all numbers correctly.

Using format r gives:

print 'e: {0:.10e}\nf: {0:.10f}\ng: {0:.10g}\nr: {0:0r}'.format(x)
ValueError: Unknown format code 'r' for object of type 'int'

Using e, f and g formats provided the following:

for x in range(123456789000,123456789019):
print 'e: {0:.10e}\nf: {0:.10f}\ng: {0:.10g}'.format(x)
e: 1.2345678900e+11
f: 123456789000.0000000000
g: 1.23456789e+11
e: 1.2345678900e+11
f: 123456789000.:000000000
g: 1.23456789e+11
e: 1.2345678900e+11
f: 123456789001.:000000000
g: 1.23456789e+11
e: 1.2345678900e+11
f: 123456789003.0000000000
g: 1.23456789e+11

I have no access to install or update anything on this server. I can request an updated version, but change requests of this nature take a fair amount of time. Also, other programs depend on this installation and a lot of testing would be required.

I have been informed that only IBM provided packages will be installed and that the latest python 2.7 package provided by IBM is 2.7.12.

I have "fixed" the problem by doing

othervar = '{0:.10f}'.format(somevar).replace(':', '0')

which is extremely unsafe, I know, but ... shrug

Argh! I just noticed an off-by-one error ... 123456789012 is being formatted as one less: 123456789011.:0000000000 ... this is a weird bug.

Answer 1

Although not an "answer", I can give you my results on a slightly newer version running on AIX.

Sorry that I'm unable to replicate your problem.

[lholtscl@ibm3 ~]$ python
Python 2.7.13 (default, Sep  7 2017, 21:08:50) [C] on aix7
Type "help", "copyright", "credits" or "license" for more information.
>>> print "%.10f" % 123456789012
123456789012.0000000000
>>> '{0:.10f}'.format(123456789012)
'123456789012.0000000000'