How to format a number with comma and specified precision digits in Python

Question

The question is for Python 2.6, that is what we have in production.

I have this requirement for formatting a number (like 1234567.0987 or 1234567.0) with comma, and specified number of digits after decimal points. So, it if precision is three, 1234567.0987 may look like 1,234,567.099.

I tried using Locale, as suggested by answers to many questions, the problem is that results in two digits after decimal, which is not acceptable for my requirement.

I tried searching in other places, but did not find any solution, and finally I created a method by my own:

def format_float(value, precision = 4):
    formatString = "%0." + str(precision) + "f"    
    str_val =  formatString % value
    first, second = str_val.split('.')
    first = int(first)
    group = []
    while True:
        result, mod = first / 1000, first % 1000
        group.append(str(mod))
        if result == 0:
            break
        first = result
    group.reverse() 
    return ','.join(group) + '.' + second

I tried to run some tests to test out the method and it works fine:

# default 4 digits precision
assert format_float(1234567890.0876543) == '1,234,567,890.0877'
assert format_float(1.2) == '1.2000'
assert format_float(1234) == '1,234.0000'
assert format_float(0) == '0.0000'

# 3 digits precision
assert format_float(1234567890.0876543, precision=3) == '1,234,567,890.088'
assert format_float(0, precision=3) == '0.000'

Being new to Python, my question is whether this is an acceptable solution. As this formatting has to be done many times in a tight for-loop, I would appreciate if someone can point to a better solution.

Thanks and Regards to All

Mark, Thank you. That is one good bug right there, I need to fix this. — cspider, Oct 10 '12 at 16:36
You don't have to use the `locale` module. See my answer to the question [_What's the easiest way to add commas to an integer in Python?_](http://stackoverflow.com/q/3909457/355230). — martineau, Oct 10 '12 at 18:11
Martin, Thanks. I upvoted your answer. However, your answer is applicable for v2.7, I am using 2.6 and that option is not available for me. — cspider, Oct 10 '12 at 19:48

Ashwini Chaudhary · Answer 1 · 2018-10-18T14:21:56.073

37

In Python 2.7 and 3.x you can use str.format for this:

>>> num = 1234567890.0876543
>>> "{0:,f}".format(num)
'1,234,567,890.087654'
>>> "{0:,.2f}".format(num)
'1,234,567,890.08'
>>> "{0:,f}".format(1234)
'1,234.000000'

edited Oct 18 '18 at 14:21

answered Oct 10 '12 at 16:30

Ashwini Chaudhary

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@kreativitea Just checked it online it does. I tried it only on python 2.6 where it doesn't worked. – Ashwini Chaudhary Oct 10 '12 at 16:36
Thanks, however, I edited my original question, that this question for Python 2.6. – cspider Oct 10 '12 at 16:39

score 23 · Accepted Answer · answered Oct 10 '12 at 16:30

23

I don't think you looked deep enough into the locale module. locale.format() is what you want, but make sure you set a locale first or you won't get grouping at all.

>>> locale.setlocale(locale.LC_ALL, '')
'en_US.UTF-8'
>>> locale.format("%.4f", 12345.678912, grouping=True)
'12,345.6789'

answered Oct 10 '12 at 16:30

cdhowie

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@cdhowie, Thank you, this works for me, even with . I glossed over the format() option. – cspider Oct 10 '12 at 16:42

How to format a number with comma and specified precision digits in Python

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