Python Decimals format

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’

Answers:

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Method 1

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

Method 2

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'

Method 3

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.

Method 4

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'

Method 5

If using 3.6 or newer, just use f-Strings

print(f'{my_var:.1f}')

Method 6

You can use “f-strings” (f for “formatted string literals”), the short format style from Python v3.6 on:

f'{1.234:.1f}'
Out: '1.2'

Or, as a test:

f'{1.234:.1f}' == '1.2'
Out: True

By the way, you can also use this with variables.

x = 1.234
f'{x:.1f} and {x:.2f} and {x}'
Out: '1.2 and 1.23 and 1.234'

If you need to use quotes in the text, embed the text with f'''...''' instead for f'...'.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0