Avoid rounding in new python string formatting

Question

I want to replace the old string formatting behaviour with the new python string formatting syntax in my scripts, but how to avoid rounding when I deal with floats?

The old version

print ('%02d:%02d:%02d' % (0.0,0.9,67.5))

yields 00:00:67

while my (obviously wrong) translation into the new syntax

print ('{0:0>2.0f}:{1:0>2.0f}:{2:0>2.0f}'.format(0.0,0.9,67.5))

yields 00:01:68.

How to avoid rounding here and get the old output with the new format syntax?

Answer 1

Explicitly convert the arguments to ints:

>>> '{:02}:{:02}:{:02}'.format(int(0.0), int(0.9), int(67.5))
'00:00:67'

BTW, you don't need to specify argument index ({0}, {1}, ..) if you use Python 2.7+, Python 3.1+ (autonumbering).

Answer 2

The "rules" are simple:

'%d' % 7.7         # truncates to 7
'%.0f' % 7.7       # rounds to 8
format(7.7, 'd')   # refuses to convert
format(7.7, '.0f') # rounds to 9

To have complete control over the presentation, you can pre-convert the float to an integer. There are several ways to do that depending on your needs:

>>> math.trunc(f) # ignore the fractional part
67
>>> math.floor(f) # round down
67
>>> math.ceil(f)  # round up
68
>>> round(f)      # round nearest
68