[Tutor] Read the builtin module source, also itchy ellipses.

Kent Johnson kent37 at tds.net
Fri Nov 17 15:10:28 CET 2006

Thomas wrote:
> Hi,
> I sometimes find it useful to read the source code of a module and for 
> example I can type string.__file__ to find the location of the string 
> module.
> However the .__file__ method is not available for the module builtin. Is 
> it possible to read the source code for built in functions and if so how 
> do I find them? I realise some/all may be written in C rather than 
> python but it would still be interesting to read them.

It's all in C, see Python\bltinmodule.c in the source distribution.
> In an unrelated follow-up may I also ask: can the ellipsis (...) be used 
> in code? I tried a googlecode search but none of the examples worked for 
> me. Can someone post an example line of code that uses ... in it. 
> This has been causing an itch in my brain, please reply with the scratch.

Syntactically ellipsis is allowed in a slice list as shown in the syntax 
definition here:

As a practical matter I think the only containers that actually support 
this kind of slicing are the arrays in Numeric and numpy. Here is a 
brief example:

You could also support this syntax in a class of your own. Here is a 
simple example that just captures the argument to __getitem__() to show 
how the mechanism works:

In [4]: class Foo(object):
    ...:     def __getitem__(self, s):
    ...:         self.s = s
    ...:         return None

In [5]: f=Foo()

In [6]: f[...,1]

In [7]: f.s
Out[7]: (Ellipsis, 1)


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