Regular expression bug?

[Peter Otten]

Ron Garret wrote:

> I'm trying to split a CamelCase string into its constituent components.

How about

>>> re.compile("[A-Za-z][a-z]*").findall("fooBarBaz")
['foo', 'Bar', 'Baz']

> This kind of works:
> 
>>>> re.split('[a-z][A-Z]', 'fooBarBaz')
> ['fo', 'a', 'az']
> 
> but it consumes the boundary characters.  To fix this I tried using
> lookahead and lookbehind patterns instead, but it doesn't work:
> 
>>>> re.split('((?<=[a-z])(?=[A-Z]))', 'fooBarBaz')
> ['fooBarBaz']
> 
> However, it does seem to work with findall:
> 
>>>> re.findall('(?<=[a-z])(?=[A-Z])', 'fooBarBaz')
> ['', '']
> 
> So the regular expression seems to be doing the Right Thing.  Is this a
> bug in re.split, or am I missing something?

IRC the split pattern must consume at least one character, but I can't find
the reference.
 
> (BTW, I tried looking at the source code for the re module, but I could
> not find the relevant code.  re.split calls sre_compile.compile().split,
> but the string 'split' does not appear in sre_compile.py.  So where does
> this method come from?)

It's coded in C. The source is Modules/sremodule.c.

Peter