Nested loop

[Steve Holden]

bonono at gmail.com wrote:
> viewcharts wrote:
> 
>>I am reading two text files comparing the values in one to the other,
>>this requires two loops. The problem is that when the inner loop is
>>finished, it never goes back into the loop. Any suggestions?
>>
>>
>>for refSymbol in symbols.readlines():
>>    for lookupSymbol in myfile.readlines():
>>        showme = lookupSymbol.split('\t')
>>        if showme[3] == refSymbol.strip():
>>            priceNew.write(refSymbol.strip()+" "+showme[10])
> 
> As another poster said, you have "used up" the inner iterable in the
> first round, it is an iterable, just not like a list where you can use
> multiple times.
> 
The result of the readlines() function *is* a list, which is precisely 
why it's been used up:

 >>> f = file("mail.py")
 >>> type(f.readlines())
<type 'list'>
 >>>

A second call to readlines just gets an empty list, since there are no 
more lines left to be read.

> Either turn it into a list(so you can reuse it) or better yet, turn it
> into a dict which would speed up the matching process. Either way, it
> better be done outside of the outer loop.
> 
The solution, as already proposed, is to bind the list of lines to a 
nanme so it can be reused.

regards
  Steve
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