Why don't we have to initialize the variable of a for loop?

Question

In Python, why don’t we have to initialize the variable of a for loop?

Answer

In Python, a for loop variable does not have to be initialized beforehand.

This is because of how Python for loops work. When it runs, the for loop statement will initialize the variable to the first character of the string, and continue updating its value to the subsequent characters in the string, until the loop reaches the final character or is terminated before that.

Example

# This initialization is not necessary!
i = 0

# i is initialized to the first character, "1"
for i in "12345":
  print(i)

# The output will be
# 1 
# 2
# 3
# 4
# 5
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by “we don’t have to initialize the variable of a for loop”
I thought you were maybe talking about this (but weren’t):

for _ in “12345”:

If the variable is never used, then you don’t have to initialize it!
Just something I thought I’d add (I just finished a course in Haskell and Rust, but never have done anything in python – so far it seems a lot easier haha)

1 Like

Does it mean Python doesn’t have/need the increment-decrement operators unlike other languages?

Not with for x in y:, which will step through an iterable (list, string, range(), many others), y and one at a time, assign its elements to x.

Other languages offer a means by which we can access the value by index, or by direct reference, just as Python does. The increment operator is typically used in a for loop of the C like languages, but not explicitly in Python. Instead we use a range object to supply a sequence of our choosing, which we may iterate.

The direction that comes from ++1 or --1 is achieved with a positive or negative direction on the range. Same effect, different means.

2 Likes

Hi, @mtf,
I’m from a java background and I generally use i++ or count++ to increment by one, but in python, I am Using
i+=1 or count+=1 for increment by one and if I use count++ in python to increment it by one like in java I get an error like (I used length as my variable here)

length++
           ^
SyntaxError: invalid syntax

so Python doesn’t support this type of operation for increment?
Thanks in advance!

Correct, the ++ and -- operators are not supported.

2 Likes