I have a simple for loop iterating through a user input string. If the it encounters a certain value, I want to be able to look ahead at the next value in order to determine what to do next. What is the best way to accomplish this? For example in my code below, if it encounters a "1" in the string, it should look at the next character in the string. If it is also a 1, print 1. Otherwise do nothing.

```
UserInput = input("Enter calculator expression:")

for x in UserInput:
    ...
    ...
    if x == 1:
#       if the next value in the string is 1:
#           print 1
#       else:
#       do nothing

```