string_encrypt.py

# Fixed version.
# Minimal changes to get it working
my_string = "This is a bunch of words!"
print(f'{my_string}')

alphabet = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'

outputStr = ''
for i in my_string:
    for idx, j in enumerate(alphabet):
        if i == j:
            outputStr += alphabet[(idx + 13) % len(alphabet)]
            break
    else:
        outputStr += i

print(f'{outputStr}')

# My attempt at the best way:
import string

all_letters = string.ascii_letters

output_list = list()
for this_letter in my_string:
    if this_letter in all_letters:
        idx = all_letters.find(this_letter)
        idx = (idx + 13) % len(all_letters)
        output_list.append(all_letters[idx])
    else:
        output_list.append(this_letter)

output_string = ''.join(output_list)
print(f'{output_string}')