'Why does this reverse the string?

def reverse(s):
  str = ""
  for i in s:
    str = i + str
  return str

I don't understand how using str in this case reverses the string?

python

Solution 1:^[1]

That's terrible naming btw. (And it's replacing the reserved keyword str).

I believe this should make it more readable. Explanations are given in the comments.

def reverse(string):
    reversed_string = ""
    for letter in string:
        reversed_string = letter + reversed_string
    
    return reversed_string

Solution 2:^[2]

Its because you prepend the characters in order. On each iteration, the i'th character becomes the first character of the result, shifting those already added to the right. In python we often use print to see what is going on. A quick change to the script shows the steps

def reverse(s):
    str = ""
    for i in s:
        print(repr(i), "+", repr(str), end="")
        str = i + str
        print(" ==>", repr(str))
    return str

print(reverse("abcd"))

Result

'a' + '' ==> 'a'
'b' + 'a' ==> 'ba'
'c' + 'ba' ==> 'cba'
'd' + 'cba' ==> 'dcba'
dcba

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution	Source
Solution 1
Solution 2

'Why does this reverse the string?

Solution 1:[1]

Solution 2:[2]

Sources

Related Questions

Solution 1:^[1]

Solution 2:^[2]