Is there a faster way to do this?

Avinash Vora avinashvora at
Tue Aug 5 18:49:54 CEST 2008

On Aug 5, 2008, at 10:00 PM, ronald.johnson at wrote:

> I have a csv file containing product information that is 700+ MB in
> size. I'm trying to go through and pull out unique product ID's only
> as there are a lot of multiples. My problem is that I am appending the
> ProductID to an array and then searching through that array each time
> to see if I've seen the product ID before. So each search takes longer
> and longer. I let the script run for 2 hours before killing it and had
> only run through less than 1/10 if the file.

Why not split the file into more manageable chunks, especially as it's  
just what seems like plaintext?

> Heres the code:
> import string
> def checkForProduct(product_id, product_list):
>    for product in product_list:
>        if product == product_id:
>            return 1
>    return 0
> input_file="c:\\input.txt"
> output_file="c:\\output.txt"
> product_info = []
> input_count = 0
> input = open(input_file,"r")
> output = open(output_file, "w")
> for line in input:
>    break_down = line.split(",")
>    product_number = break_down[2]
>    input_count+=1
>    if input_count == 1:
>        product_info.append(product_number)
>        output.write(line)
>        output_count = 1

This seems redundant.

>    if not checkForProduct(product_number,product_info):
>        product_info.append(product_number)
>        output.write(line)
>        output_count+=1

File writing is extremely expensive.  In fact, so is reading.  Think  
about reading the file in whole chunks.  Put those chunks into Python  
data structures, and make your output information in Python data  
structures.  If you use a dictionary and search the ID's there, you'll  
notice some speed improvements as Python does a dictionary lookup far  
quicker than searching a list.  Then, output your data all at once at  
the end.


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