Fastest way to calculate leading whitespace

[Steven D'Aprano]

On Sat, 08 May 2010 12:15:22 -0700, Wolfram Hinderer wrote:

> On 8 Mai, 20:46, Steven D'Aprano <st... at REMOVE-THIS- cybersource.com.au>
> wrote:
> 
>> def get_leading_whitespace(s):
>>     t = s.lstrip()
>>     return s[:len(s)-len(t)]
>>
>> >>> c = get_leading_whitespace(a)
>> >>> assert c == leading_whitespace
>>
>> Unless your strings are very large, this is likely to be faster than
>> any other pure-Python solution you can come up with.
> 
> Returning s[:-1 - len(t)] is faster.


I'm sure it is. Unfortunately, it's also incorrect.


>>> z = "*****abcde"
>>> z[:-1-5]
'****'
>>> z[:len(z)-5]
'*****'


However, s[:-len(t)] should be both faster and correct.


-- 
Steven