Theoretical doubt about while and indentation

Question

count = 0
while (count < 10):
    # Ponto A
    print ("Olá...", count)
    count =  count + 1
    # Ponto B
# Ponto C

Why

Count < 10 is always true at point B.

is not true if the "Point B" belongs to the same indentation of the "Point A" inside the while?

Another question:

i = 6
while (i > 0):
    i = i - 3
    print (i)

Why the output is 3 and 0 and not only 3?

Thank you very much!

Answer 1

You asked why in the code below:

(1) i = 6
(2) while (i > 0):
(3)   i = i - 3;
(4)   print (i)

The output is 3 and 0 and not only 3. The answer is simple, but requires you to consider how Python interprets each command line. For ease, I listed the lines in the code above, ok?

The first line executed is (1). It simply assigns the value 6 to the variable i. The second line executed is (2). It checks if i > 0, and since i is worth 6 (at this time), this is true and Python allows execution to enter the loop. Thus, the next line executed is (3), which causes i to receive i - 3. As at this time i is worth 6, the result is i = 6 - 3, so i = 3. This value is printed on the next line, as expected.

The execution then returns to line (2). The current value of i is 3 (which incidentally was the last printed). Since i > 0 (because 3 > 0) is true, the processing enters the loop again. The line (3) does the subtraction again, causing i to be set to 0 (since it does i = 3 - 3). Line (4) then prints the current value of i, which is 0.

Finally the execution returns to the line (2), but this time the processing does not enter the loop because the condition is no longer true.

Try running this code:

i = 6
while True:
  i = i - 3
  if(i > 0):
    print (i)
  else:
    break

Note that in this code the condition of the loop is in fact always true (after all, it is fixed True), and the correct condition (its original condition) was moved into the loop in a if. Analyze with this new code how the computer processes line by line sequentially, following the current value of the variable in each step (this procedure usually - or used to - be called "table test"). It will help you understand how "logic" influences problem solving. :)

Answer 2

Count < 10 is always true at point B.

Actually it is not. At point B Count will be the previous Count +1. Its maximum will be 9, because while stops if Count equals 10. Test your script.

i = 6
while (i > 0):
  i = i - 3;
  print (i)

First: The indentation used is outside the recommendations. Inside a loop, function, class or whatever, the recommended and commonly used are 4 spaces. This is important to maintain a standardization and good visual organization of the code, so if other people are using the code, they will be familiar with formatting.
According to: The semicolon is unnecessary.
Third and answer to the question: Think like the script:
The ienters the loop as 6, becomes 3 and is printed. The loop resumes with the i like 3, becomes 0 and is printed again. Only then i is tested again (this time being 0) and does not enter the loop.