Python 3 - Check letters in string with the next letter

Question

If I have a string

String = 'ABCEEFGH'

How can I check what letter is beside each letter without going out of index?

for index in range(len(String)):
    if String[index] == String[index+1]: 
        print('Double')

Answer 1

You can use enumerate, slicing the string up to the second last character:

String = 'ABCEEFGH'

for ind,ch in enumerate(String[:-1]):
    if ch == String[ind+1]:
        print('Double')

In your own code the logic would be the same len(String)-1 but enumerate is the way to go:

for index in range(len(String)-1):
    if String[index] == String[index+1]:
        print('Double')

The fact you seen to only want to check if any two adjacent characters are identical, maybe using any would be best:

String = 'ABCEEFGH'

if any( ch == String[ind+1] for ind, ch in enumerate(String[:-1])):
        print('Double',ch)

any will short circuit and break the loop as soon the condition is Trueor else evaluate to False if we have no match.