[Tutor] Please look at my wordFrequency.py

[Kent Johnson]

Andrew P wrote:
> Just want to add a little something here, because reading over this 
> thread, I think there may have been some confusion:
> 
> Kent wrote:
> 
> for e in saveRemovedForLaterL:
>    L.append(e)
> could be
> L.extend(e)
> 
> I think he might have meant:
> 
> for e in saveRemovedForLaterL:
>    L.append(e)
> could be
> L.extend(saveRemovedForLaterL)

Right you are, thanks for the catch!

Kent

> 
> The difference between these is that one is explicitly looping with 
> Python, accessing each element of the first list one at a time, 
> appending it to the other one at a time.  Whereas if you call extend() 
> instead, it will be doing that looping for you with the extend() method, 
> written in C, and very quickly indeed.  I would worry less about what is 
> written in C vs what is built-in, and does implicit looping for you.  
> Any time you can avoid stepping over a list one element at a time, is 
> usually the faster way.
> 
>  >>> lst = [1,2,3,4]
>  >>> lst2 = [5,6,7,8]
>  >>> lst.extend(lst2)
>  >>> print lst
> [1, 2, 3, 4, 5, 6, 7, 8]
> 
> Compare this to:
> 
>  >>> lst = [1,2,3,4]
>  >>> lst2 = [5,6,7,8]
>  >>> for num in lst2:
> ...     lst.append(num)  
>  >>> print lst
> [1, 2, 3, 4, 5, 6, 7, 8]
> 
> 
> FWIW, append is generally used to generate a list from something 
> calculated on the fly:
> 
>  >>> lst = []
>  >>> for i in range(10):
> ...     lst.append(i)
> ...    
>  >>> print lst
> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
> 
> 
> 
>     Ah. But how can I know what is in C code and what isn't? For example, in
>     a previous post you say that L.extend(e) is in C, and imply that
>     L.append(e) isn't, and that therefore L.extend(e) should be used.
> 
>     Well, back to Hetlands' Beginning Python.
> 
>     Dick
> 
> 
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