jcarlson at uci.edu
Thu Oct 21 08:31:45 CEST 2004
"Chris S." <chrisks at NOSPAM.udel.edu> wrote:
> Is there a purpose for using trailing and leading double underscores for
> built-in method names? My impression was that underscores are supposed
> to imply some sort of pseudo-privatization, but would using
> myclass.len() instead of myclass.__len__() really cause Python
> considerable harm? As much as I adore Python, I have to admit, I find
> this to be one of the language's most "unPythonic" features and a key
> arguing point against Python. I've searched for a discussion on this
> topic in the groups archives, but found little. What are everyone's
> thoughts on this subject?
Double underscore methods are considered "magic" methods. The
underscores are a hint that they may do something different. Kind of
like the C++ friend operators.
In terms of .len() vs .__len__(), it is not supposed to be called
directly by user code; __len__() is called indirectly by the len()
builtin (and similarly for the other __<op>__() methods, check common
spellings in the operator module).
a = foo()
len(a) #like this
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