Python 3 Object-Oriented Programming - Third Edition

Enumerate

Sometimes, when we're looping over a container in a for loop, we want access to the index (the current position in the list) of the current item being processed. The for loop doesn't provide us with indexes, but the enumerate function gives us something better: it creates a sequence of tuples, where the first object in each tuple is the index and the second is the original item.

This is useful if we need to use index numbers directly. Consider some simple code that outputs each of the lines in a file with line numbers:

import sysfilename = sys.argv[1]with open(filename) as file:    for index, line in enumerate(file):        print(f"{index+1}: {line}", end="")

Running this code using its own filename as the input file shows how it works: