import overwrites __name__

[Peter Otten]

Piet van Oostrum wrote:

>>>>>> Peter Otten <__peter__ at web.de> (PO) wrote:
> 
>>PO> $ cat x.py
>>PO> import sys
>>PO> globals().update(zip(*(range(110),)*2))
>>PO> y = 42
>>PO> print __name__
>>PO> if __name__ == "__main__":
>>PO>     a = b = 42
>>PO> print len(dir())
>>PO> from x import y as z
>>PO> try:
>>PO>     print my_name
>>PO> except NameError, e:
>>PO>     print 'unhandled NameError: "%s"' % e
>>PO>     sys.exit()
> 
>>PO> $ python x.py
>>PO> __main__
>>PO> 119
>>PO> x
>>PO> 117
>>PO> unhandled NameError: "name 'my_name' is not defined"
> 
> This is perfectly normal. 

I'm not 100% sure of that.

Just in case you didn't notice: I'm not the OP. The above piece of junk code 
was my attempt to keep as close to the code he posted while producing the 
same output that he got.

> python x.py command runs normally (although
> the globals().update is a very weird thing to do), until the from x
> import y command. Then x.py is loaded again but now as the module 'x'
> instead of '__main__'. Python doesn't know it's the same file, and
> actually it doesn't want to know. It only knows it when you do import
> twice on the same file. Not when you run it as a main script first and
> then imports it. **This is a thing you shouldn't do**.
> There are now two namespaces: one for __main__ and one for x. These are
> distinct and have no relationship.
> 
> The reason that the first number is 119 and the second is 117 is that
> while importing x the variables a and b are not created.

Your explanation is of course between 119 and 117% correct while I was only 
99% serious...

Cheers,
Peter