Python Decimals format

Question

WHat is a good way to format a python decimal like this way?

1.00 --> '1'
1.20 --> '1.2'
1.23 --> '1.23'
1.234 --> '1.23'
1.2345 --> '1.23'

Answer 1

Just use Python's standard string formatting methods:

>>> "{0:.2}".format(1.234232)
'1.2'
>>> "{0:.3}".format(1.234232)
'1.23'

If you are using a Python version under 2.6, use

>>> "%f" % 1.32423
'1.324230'
>>> "%.2f" % 1.32423
'1.32'
>>> "%d" % 1.32423
'1'

Answer 2

Here's a function that will do the trick:

def myformat(x):
    return ('%.2f' % x).rstrip('0').rstrip('.')

And here are your examples:

>>> myformat(1.00)
'1'
>>> myformat(1.20)
'1.2'
>>> myformat(1.23)
'1.23'
>>> myformat(1.234)
'1.23'
>>> myformat(1.2345)
'1.23'

Edit:

From looking at other people's answers and experimenting, I found that g does all of the stripping stuff for you. So,

'%.3g' % x

works splendidly too and is slightly different from what other people are suggesting (using '{0:.3}'.format() stuff). I guess take your pick.

Answer 3

Step 1: round the number, or simply trim it to two decimal places.

Step 2: convert it to a string.

Step 3: remove the trailing zero that it could have (if it were '1.0' or '1.20', for instance).

Step 4: remove the trailing decimal point that it could have (if it were '1.' after removing a trailing zero, for instance).

Here it is:

import re

float = <whatever>
rounded = str(round(float, 2))
replaceTrailingZero = re.compile('0$')
noTrailingZeros = replaceTrailingZeros.sub('', rounded)
replaceTrailingPeriod = re.compile('\.$')
finalNumber = replaceTrailingPeriod.sub('', noTrailingZeros)

Answer 4

If you have Python 2.6 or better, use format:

'{0:.3g}'.format(num)

For Python 2.5 or worse:

'%.3g'%(num)

Explanation:

{0}tells format to print the first argument -- in this case, num.

Everything after the colon (:) specifies the format_spec.

.3 sets the precision to 3.

g removes insignificant zeros. See http://en.wikipedia.org/wiki/Printf#fprintf

For example:

tests=[(1.00,'1'),
       (1.2,'1.2'),
       (1.23,'1.23'),
       (1.234,'1.23'),
       (1.2345,'1.23')]

for num,answer in tests:
    result='{0:.3g}'.format(num)
    if result != answer:
        print('Error: {0} --> {1} != {2}'.format(num,result,answer))
        exit()
    else:
        print('{0} --> {1}'.format(num,result))

yields

1.0 --> 1
1.2 --> 1.2
1.23 --> 1.23
1.234 --> 1.23
1.2345 --> 1.23