# Splitting a string into substrings of equal size

MRAB python at mrabarnett.plus.com
Sun Aug 16 00:06:22 CEST 2009

```ryles wrote:
> On Aug 14, 8:22 pm, candide <cand... at free.invalid> wrote:
>> Suppose you need to split a string into substrings of a given size (except
>> possibly the last substring). I make the hypothesis the first slice is at the
>> end of the string.
>> A typical example is provided by formatting a decimal string with thousands
>> separator.
>>
>> What is the pythonic way to do this ?
>>
>> For my part, i reach to this rather complicated code:
>>
>> # ----------------------
>>
>> def comaSep(z,k=3, sep=','):
>>     z=z[::-1]
>>     x=[z[k*i:k*(i+1)][::-1] for i in range(1+(len(z)-1)/k)][::-1]
>>     return sep.join(x)
>>
>> # Test
>> for z in ["75096042068045", "509", "12024", "7", "2009"]:
>>     print z+" --> ", comaSep(z)
>>
>> # ----------------------
>>
>> outputting :
>>
>> 75096042068045 -->  75,096,042,068,045
>> 509 -->  509
>> 12024 -->  12,024
>> 7 -->  7
>> 2009 -->  2,009
>>
>> Thanks
>
> py> s='1234567'
> py> ','.join(_[::-1] for _ in re.findall('.{1,3}',s[::-1])[::-1])
> '1,234,567'
> py> # j/k ;)

If you're going to use re, then:

>>> for z in ["75096042068045", "509", "12024", "7", "2009"]:
print re.sub(r"(?<=.)(?=(?:...)+\$)", ",", z)

75,096,042,068,045
509
12,024
7
2,009

```