Function to remove elements from a list working, but Python Hangs :((

[Steve Holden]

Girish Sahani wrote:
>>I guess it's already the case with lst = [ e for e in lst if e in pairs ]
>>
>>
>>In [1]: lst = (1,2,3,4)
>>
>>In [2]: pairs=(5,)
>>
>>In [3]: lst=[e for e in lst if e in pairs]
>>
>>In [4]: lst
>>Out[4]: []
> 
> Yes its working. I realized that i was giving an input which didnt satisfy
> the condition.
> Now if you could please check out this new problem i'm facing,related to
> this.In my code,l4 is a list of lists, and these lists contain such pairs.
> e.g. l4 =
> [[[4,2],[4,7],[4,10],[4,12],[9,2],[9,7],[9,10],[9,12],[11,2],[11,10]],[[1,2],[3,5],[7,8]]]
> which is a list of 2 lists (having 13 pairs)
> Now when l4 has 50 pairs, and i run the code, python just hangs, and i'm
> quite sure its because of this. Is there any way to rectify this???
> 
Yes: use standard debugging techniques.

You might try adding "print" statements to show you the value of various 
names as you run through the code: frequently this is good enough to 
explain what's going wrong (although you *do* need enough confidence to 
be able to predict what the values should be).

If all else fails try the "stuffed bear" technique: sit an inanimate 
object in front of you and explain the code, and exactly why it can't 
possibly be going wrong. Amazingly often, halfway through your 
explanation you realise what your error is.

regards
  Steve
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