On Wednesday 18 August 2010, it occurred to Brandon Harris to exclaim:
> Having trouble using %s with re.sub
>
> test = '/my/word/whats/wrong'
> re.sub('(/)word(/)', r'\1\%s\2'%'1000', test)
>
> return is /my/@0/whats/wrong
>
This has nothing to do with %, of course:
>>> re.sub('(/)word(/)', r'\1\%d\2'%1000, test)
'/my/@0/whats/wrong'
>>> re.sub('(/)word(/)', r'\1\1000\2', test)
'/my/@0/whats/wrong'
let's see if we can get rid of that zero:
>>> re.sub('(/)word(/)', r'\1\100\2', test)
'/my/@/whats/wrong'
so '\100' appears to be getting replaced with '@'. Why?
>>> '\100'
'@'
This is Python's way of escaping characters using octal numbers.
>>> chr(int('100', 8))
'@'
How to avoid this? Well, if you wanted the literal backslash, you'll need to
escape it properly:
>>> print(re.sub('(/)word(/)', r'\1\\1000\2', test))
/my/\1000/whats/wrong
>>>
If you didn't want the backslash, then why on earth did you put it there? You
have to be careful with backslashes, they bite ;-)
Anyway, you can simply do the formatting after the match.
>>> re.sub('(/)word(/)', r'\1%d\2', test) % 1000
'/my/1000/whats/wrong'
>>>
Or work with match objects to construct the resulting string by hand.
- Thomas
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