[Tutor] list comprehension, testing for multiple conditions

[Peter Otten]

Pete O'Connell wrote:

[Please don't to-post. Clip all text of previous posts except the portion 
relevant to your question]

> Hi. The next step for me to parse the file as I want to is to change
> lines that look like this:
> f 21/21/21 22/22/22 24/24/23 23/23/24
> into lines that look like this:
> f 21 22 23 24
> 
> Below is my terribly slow loop for doing this. 

I'd say you are not yet at the point where you should care for speed too 
much. Build the complete tool-chain with tests to verify correctness and 
then measure execution time to find the bottlenecks.

> Any suggestions about
> how to make this code more efficient would be greatly appreciated
> 
> 
################################################################################
> fileName = '/usr/home/poconnell/Desktop/objCube.obj'
> 
> with open(fileName) as lines:
>     theGoodLines = [line.strip("\n") for line in lines if "vn" not in
> line and "vt" not in line and line != "\n"]
> 
> for i in range(len(theGoodLines)):
>     if theGoodLines[i][0] == "f":
>         aGoodLineAsList = theGoodLines[i].split(" ")
>         theGoodLines[i] = aGoodLineAsList[0] + " " +
> aGoodLineAsList[1].split("/")[-1] + " " +
> aGoodLineAsList[2].split("/")[-1] + " " +
> aGoodLineAsList[3].split("/")[-1] + " " +
> aGoodLineAsList[4].split("/")[-1]
> 
> for anItem in theGoodLines:
>     print anItem

If your sample data is representative you don't need most of the filtering:

fileName = ...
with open(fileName) as lines:
    for line in lines:
        if line.startswith("f "):
            print " ".join(part.rpartition("/")[-1] for part in 
line.split())