Can't count iterations on double for loop in python

Question

I am having trouble implementing a counter to count over iterations on a double for loop.

My code is the following:

def encode(mat,l,c,mode,m):
    sampleCount = 0
    for i in range(l):
        for j in range(c):
            sampleCount += 1

    print(sampleCount)

My program calls this function with values of "l" of 720 and 360 and values of "c" of 1280 and 640 respectively. What I was expecting was sampleCount values of 921600 and 230400. However, it prints either 1279 or 639. Also, when i tested printing i and j like this:

for i in range(l):
    print(i)
    for j in range(c):
        print(j)

What I get is the program printing all the i values, from 0 to l-1 and only then printing the j values from 0 to c-1.

Can anyone tell me what I may be doing wrong? Thanks in advance!

Edit: Pasted code without identation

Edit 2: Tried commenting everything after sampleCount += 1. In that case, i obtain the expected results. And it continues to work well if i uncomment the following two lines of code. However, when i tried uncommenting more than 3 lines of code, it goes back to misbehaving. In short, it works when the code is like this:

def encode2(mat,l,c,mode,m):
    sampleCount = 0
    for i in range(l):
        for j in range(c):
            sampleCount += 1
            a = 0
            b = 0
            # c = 0
            # x = 0
            # if (i == 0 & j == 0):
            #     a = 0
            #     b = 0
            #     c = 0
         ...  ...

And misbehaves again if the code is like this:

def encode2(mat,l,c,mode,m):
    sampleCount = 0
    for i in range(l):
        for j in range(c):
            sampleCount += 1
            a = 0
            b = 0
            c = 0
            # x = 0
            # if (i == 0 & j == 0):
            #     a = 0
            #     b = 0
            #     c = 0
         ...   ...

Well, i print them before calling the function and I know they are values of 1280 or 640 and 720 or 360 for l and c respectively. This code is part of a video encoder and my objective is to go through each of the "pixels" of the frame — Nuno Fernandes
– Nuno Fernandes, Commented Jan 6, 2020 at 14:09
Sounds like an indentation problem from the symptoms, you describe the second loop happens after the first completed, so I guess the interpreter doesn't see the relation between them as you expect — Eyal H
– Eyal H, Commented Jan 6, 2020 at 14:14
your encode function is empty. You are probably getting an error for having an empty function. Try solving this first — user2261062
– user2261062, Commented Jan 6, 2020 at 14:22
Sorry, I pasted the code wrong. In the program, the identation is correct. I will edit it — Nuno Fernandes
– Nuno Fernandes, Commented Jan 6, 2020 at 14:28
You are doing range(c) and inside the loop you do c=0. You cannot do that, the loop is using the variable c. — user2261062
– user2261062, Commented Jan 6, 2020 at 15:47

Vaibhav Jadhav · Accepted Answer · 2020-01-06 14:28:32Z

1

I got the following result when I ran the same code:

def encode(l,c):
    sampleCount = 0
    for i in range(l):
        for j in range(c):
            sampleCount += 1

    print(sampleCount)
encode(360,640)

Result: 230400

def encode(l,c):
    sampleCount = 0
    for i in range(l):
        for j in range(c):
            sampleCount += 1

    print(sampleCount)
encode(720,1280)

Result: 921600

The same is your expectation?

answered Jan 6, 2020 at 14:28

Vaibhav Jadhav

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4 Comments

Nuno Fernandes Over a year ago

Yes, that is what i hoping to get. One thing I didn't mention is that there is more code after the sampleCount += 1. A bunch of variable assignments and if conditions, but with no breaks nor continues

user2261062 Over a year ago

Then most probably you are redefining some variable there, maybe you are reusing i or j for other purposes.

Vaibhav Jadhav Over a year ago

I saw your code. You are changing the value of c in c=0 which is being used for loop iteration i.e. range(c). So the loop count changes. And you are getting the wrong answer.

Nuno Fernandes Over a year ago

@VaibhavJadhav YES! That's exactly it! I feel so stupid right now. Thanks so much!!

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