They don't; it's purely a matter of convention that Python style guides prefer under_scored over camelCased. But you are entirely free to implement all of your python functions and variables and whatnot in camelCase, and in fact, many libraries do.

You could probably even try to write a decorator that converted under_scores function names to camelCase for a nice little introduction into various parts of some of the more internal pieces of python.

uhmm, AFAIK pep8 suggest UpperCamelCase for classes, under_score for packages, methods and functions[0]

btw: it's not a decorator :) but a camelCase->under_score renamer it's pretty easy to write

    import re
    
    def unCamel(obj, *maybe_camels):
        if not maybe_camels:
            maybe_camels = filter(lambda n: not n.startswith('_'), dir(obj))
    
        for maybe_camel in maybe_camels:
            underscore = re.sub(r'([^A-Z])([A-Z])([^A-Z])',
                lambda m: '%c_%c%c' % (m.group(1), m.group(2).lower(), m.group(3)),
                maybe_camel)
            if underscore != maybe_camel:
                setattr(obj, underscore, getattr(obj, maybe_camel))
    
    if __name__ == '__main__':
        class CamelCase(object):
            def multiWordMethod(self):
                print('called multiWordMethod')
        
        def multiWordFunction():
            print('called multiWordFunction')
    
        unCamel(CamelCase)    # magic
        import sys
        unCamel(sys.modules[__name__], 'multiWordFunction')    # magic
    
        CamelCase().multi_word_method()
        multi_word_function()

[0] http://www.python.org/dev/peps/pep-0008/

Even in python standard library there are mixtures ie threading.Thread. Although those (as I understand it) are just remnants of old implementation that is kept for backwards compatibility.

Isn't that normal? I though lowercase module name, uppercase class was the standard casing.

threading.Thread would seem to be consistent with the Google Python Style Guide (threading = module, Thread = Class)

http://google-styleguide.googlecode.com/svn/trunk/pyguide.ht...

the methods of threading.Thread are camel case (ie getName)

http://docs.python.org/2/library/threading.html

Yes, I think they ought to provide both styles;

Providing the camelCase will allow whole swathes of JS code to be cut-n-pasted; that code would be legal Python as well as JS.