Python Decimals format

If you have Python 2.6 or newer, use format:

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

For Python 2.5 or older:

'%.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 --> 11.2 --> 1.21.23 --> 1.231.234 --> 1.231.2345 --> 1.23

Using Python 3.6 or newer, you could use f-strings:

In [40]: num = 1.234; f'{num:.3g}'Out[40]: '1.23'

Only first part of Justin's answer is correct.Using "%.3g" will not work for all cases as .3 is not the precision, but total number of digits. Try it for numbers like 1000.123 and it breaks.

So, I would use what Justin is suggesting:

>>> ('%.4f' % 12340.123456).rstrip('0').rstrip('.')'12340.1235'>>> ('%.4f' % -400).rstrip('0').rstrip('.')'-400'>>> ('%.4f' % 0).rstrip('0').rstrip('.')'0'>>> ('%.4f' % .1).rstrip('0').rstrip('.')'0.1'

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.