Learning Python - 4th day (Night - 2)

 Watched this tutorial: Click Here

I have learned about Continue, Break and Pass statements.

Let's imagine I have a scenario where I am cycling and I see a bunch of rude people walking through the road after every 10 - 15 seconds. I just have to ignore them.

So while I am cycling
     If I see rude people
          I will just continue cycling

Also while cycling I often see animals like cat and dogs cross the road.

So while I am cycling
    If I see animal crossing road
         I will break and stop cycling

In another scenario, if I see a hole in the road, I just have to pass by the hole carefully

So while I am cycling
    If I see a hole in the road
         I will pass by the hole

Just like previous 3 examples Continue, Break, Pass works to stop or to let the loop run.

Let's have a real example in Python:

Goal is, I want to print all the values from 1 to 20 which are dividable by 3

In normal sentence, I can say like 

While the number is less than 20:
    if the number modulus by 3 is not 0
        then continue
    Print the number

What this will do is ignore the while loop whenever the number is undividable by 3

Same happens with break and pass, the difference is Break leaves the loop forever and pass ignores a certain condition

More examples of them:

4.4. break and continue Statements, and else Clauses on Loops

The break statement, like in C, breaks out of the innermost enclosing for or while loop.

Loop statements may have an else clause; it is executed when the loop terminates through exhaustion of the iterable (with for) or when the condition becomes false (with while), but not when the loop is terminated by a break statement. This is exemplified by the following loop, which searches for prime numbers:

>>>

>>> for n in range(2, 10):
...     for x in range(2, n):
...         if n % x == 0:
...             print(n, 'equals', x, '*', n//x)
...             break
...     else:
...         # loop fell through without finding a factor
...         print(n, 'is a prime number')
...
2 is a prime number
3 is a prime number
4 equals 2 * 2
5 is a prime number
6 equals 2 * 3
7 is a prime number
8 equals 2 * 4
9 equals 3 * 3

(Yes, this is the correct code. Look closely: the else clause belongs to the for loop, not the if statement.)

When used with a loop, the else clause has more in common with the else clause of a try statement than it does with that of if statements: a try statement’s else clause runs when no exception occurs, and a loop’s else clause runs when no break occurs. For more on the try statement and exceptions, see Handling Exceptions.

The continue statement, also borrowed from C, continues with the next iteration of the loop:

>>>

>>> for num in range(2, 10):
...     if num % 2 == 0:
...         print("Found an even number", num)
...         continue
...     print("Found an odd number", num)
...
Found an even number 2
Found an odd number 3
Found an even number 4
Found an odd number 5
Found an even number 6
Found an odd number 7
Found an even number 8
Found an odd number 9

4.5. pass Statements

The pass statement does nothing. It can be used when a statement is required syntactically but the program requires no action. For example:

>>>

>>> while True:
...     pass  # Busy-wait for keyboard interrupt (Ctrl+C)
...

This is commonly used for creating minimal classes:

>>>

>>> class MyEmptyClass:
...     pass
...

Another place pass can be used is as a place-holder for a function or conditional body when you are working on new code, allowing you to keep thinking at a more abstract level. The pass is silently ignored:

>>>

>>> def initlog(*args):
...     pass   # Remember to implement this!
...