pytutorial/python_basics/while/README.md

Flow Control while, pass, break, continue

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* TOC {:toc}

The goal

While we wait...

Questions to David Rotermund

Logic blocks need to be indented.​ Preferable with 4 spaces!

The while statement

i = 0​
while i < 3:​
    print(i)​
    i += 1

Output

0​
1​
2

The full statement

while_stmt ::=  "while" assignment_expression ":" suite
                ["else" ":" suite]

pass

Since Python uses indents as definition for a functional block it needs pass for signaling an empty functional block. ​

pass is a null operation — when it is executed, nothing happens. It is useful as a placeholder when a statement is required syntactically, but no code needs to be executed

pass_stmt ::=  "pass"

break

break may only occur syntactically nested in a for or while loop, but not nested in a function or class definition within that loop.

It terminates the nearest enclosing loop, skipping the optional else clause if the loop has one.

If a for loop is terminated by break, the loop control target keeps its current value.

break_stmt ::=  "break"

for i in range(0, 5):​
    if i == 2:​
        break​
    print(i)

Output:

0
1

continue

continue may only occur syntactically nested in a for or while loop, but not nested in a function or class definition within that loop. It continues with the next cycle of the nearest enclosing loop.

continue_stmt ::=  "continue"

for i in range(0, 5):​
    if i == 2:​
        continue​
    print(i)

Output:

0
1
3
4