String Mirror Function

Question

I wanted to write a function that mirrors a string without using any built in functions and only using a loop.

For example, wordMirror("stackexchange") returns 'stackexchangeegnahcxekcats'.

I wrote the following code using some hints from my previous questions:

def wordMirror(word):
    c = ""
    for x in word:
        c = c + x
    return word + c

But it didn't work. I then started to play around with it and just reversed c = c + x to c = x + c and it magically worked.

What exactly is the code reading when I switched the variables?

Answer 1

There is nothing magic about it, the order in which your are adding characters to c is reversed because you are inserting x before what was previously in c.

You should really step through a run by hand:

iteration  |   x   |    c 
-------------------------------
0             ''       ''
1              s        s
2              t        ts 
3              a        ats
4              c        cats
5              k        kcats
6              e        ekcats
7              x        xekcats
8              c        cxekcats
9              h        hcxekcats
10             a        ahcxekcats
11             n        nahcxekcats
12             g        gnahcxekcats
13             e        egnahcxekcats

From this simple table you should be able to see how the string is growing. Learning how to execute your programs by hand is a vital skill to have.