pySwapPairs

# Function to accept a string and swap pairs of characters
# Mike Kerry - Feb 2021 - acclivity2@gmail.com

# Examples
# "hello world" becomes "ehll oowlrd"
# "behave now" becomes "ebahevn wo"


def swap_pairs(s1):                     # Define a function to do the work. "s1" contains the string to be processed

    # We cannot directly change the input string, because strings in Python are "immutable" (cannot be modified)

    s2 = ""                             # initialise a new empty string
    for x in range(0, len(s1)-1, 2):    # start a loop counting in twos through the input string
                                        # but make sure we won't try to access a character beyond the end

        s2 += s1[x+1]                   # add the 2nd character of a pair to our new string
        s2 += s1[x]                     # add the first character of a pair to our new string
                                        # loop back to process the next pair

    if len(s1) & 1:                     # If the input string had an odd number of characters ...
        s2 += s1[-1]                    # ... then append the last remaining character to our new string

    return s2                           # exit from the function, returning the new completed string


tests = ["hello world", "behave now"]   # define a list of strings to be processed by our function

for test_string in tests:               # extract one string at a time
    result = swap_pairs(test_string)    # pass a string to our function and get the returned string
    print(test_string, " >> ", result)  # print the original string and the processed string

# Output:
# hello world  >>  ehll oowlrd
# behave now  >>  ebahevn wo