python - .replace() index use as variable for a loop

Question

hi everyone! I am a beginner and I can't find answer for this:

one = [" January ", " February ", " March ", " April ", " May ", 
        " June ", " July ", " August ", " September ", " October ", 
        " November ", " December ", "   ", "IPS", "COL", "BRT"]

two = ["/01/", "/02/", "/03/", "/04/", "/05/", "/06/", "/07/", "/08/",
        "/09/", "/10/", "/11/", "/12/", ",", "", "", ""]

a = len(one)     
b = len(two)

while a>0:
    text = open("database.txt", "r")
    text = ''.join([i for i in text]).replace(one[a], two[a])
    x = open("new_database.txt","w")
    x.writelines(text)
    x.close()
    a = a - 1

the error is:

    text = ''.join([i for i in text]).replace(one[a], two[a])
IndexError: list index out of range

if anyone can help, much appreciated!

question from:https://stackoverflow.com/questions/65893597/replace-index-use-as-variable-for-a-loop

Answer 1

The error is because list indexes are zero-based, so the valid indexes of one are 0 through len(one)-1. Since you initiaze a to len(one), it's outside the range.

But instead of manually assigning index variables and decrementing them, you should just loop through the list elements. You can use zip() to loop through two lists in parallel.

Here's a better way to write it:

with open("database.txt", "r") as indb, open("new_database.txt", "w") as outdb:
    for line in indb:
        for old, new in zip(one, two):
            line = line.replace(old, new)
        outdb.write(line)