When to use python's enumerate() instead of range() in loops

The range() function is often useful when iterating over a set of integers:

for n in range(50):
    ...

#

for n in range(10, 30):
    ...

or a list of strings:

for fruit in ["apple", "mango", "banana"]:
    ...

Now, say you want to iterate over the list of fruits and also show the index of the current item in the list. Using range(), this might be done like this:

fruits = ["apple", "mango", "banana"]

for i in range(len(fruits)):
    fruit = fruits[i]
    print(f"{i}: {fruit}")

# Output:
# 0: apple
# 1: mango
# 2: banana

It gets the job done, but not very pythonic. You have to get the length of the list to keep track of the index, then index into the array to get the current fruit - which makes the code more verbose and harder to read.

A better way: enumerate()

fruits = ["apple", "mango", "banana"]

for i, fruit in enumerate(fruits):
    print(f"{i}: {fruit}")

# Output:
# 0: apple
# 1: mango
# 2: banana

Numbering can also be set to begin at any desired number.

fruits = ["apple", "mango", "banana"]

for i, fruit in enumerate(fruits, 7):
    print(f"{i}: {fruit}")

# Output
# 7: apple
# 8: mango
# 9: banana