PYTHON REVISION TOUR – I

Iteration is the repetition of a process in order to generate an outcome. Iterative statements or loops enable a program with a cyclic flow of logic. Each statement which is written under the scope of a looping statement gets executed the number of times the iteration/looping continues for. There are two basic types of looping statements available in Python, they are as follows.

• while() Loop

A while() loop tests for its ending condition before executing the statements enclosed in the loop body even the first time. Syntax while(loop-condition): statement(s)
A while continues iteration cycle till its loop condition is evaluated as true. If the loop-condition is false, then loop will not execute even once.

In while() loop, the looping condition is evaluated at the beginning of the loop’s scope, i.e. prior to entering into the scope of loop. This type of checking is called “Entry control checking”, if the condition fails this checking, then the entry into the scope of loop will not be allowed. So, while () loops are often called as Entry Control Loop.
The while() loop can accept expression and not just conditions, the following are all illegal expressions:

(i) while(x = x + 1)
(ii) while (n–)
(iii) while(count + =î)
When the result of x = x + 1, nor count += i, evaluates to 0, then the while condition fails and the loop will exit.

• for () Loop

The for statement encloses one or more statements that form the body of the loop, the statements in the loop repeat continuously a certain number of times.
This loop is also known as entry control loop, as condition is checked before entering into the scope of the loop.

Syntax
for(variable) in <sequence>: statement(s)
or range (start, stop, step): for(variable) in range. statement(s)

• nested Loop

When a loop may contain another loop in its body is called nested loop. Any conditional statement can be nested within any other conditional statement. In nested loop, two loops; inner loop and outer loop are executed. But the inner loop must terminate before the outer loop.
Syntax for<variable> in <sequence>: for<variable> in <sequence>: statements
e.g. for i in range (1,6,+2): for j in range (1.1,+1): print(i, “”, j)

• JUMP STATEMENTS

Jump statements allow altering the flow of a program by performing jumps to specific locations.
The jump statements defined in Python are break and continue.

• break Statement

The break statement alters the normal flow of execution as it terminates the current loop and resumes execution of the statement following that loop.
It can also be used to stop executing further statements inside the body of conditional statements. break statement used in a nested loop affects only the inner loop in which it is used and not any of the outer loops.
Syntax
break

• continue Statement

When a continue statement is encountered, the control skips the execution of remaining statements inside the body of the loop for the current iteration and jumps to the beginning of the loop for the next iteration. If the loop’s condition is still True, the loop is entered again, else the control is immediately following the loop. transferred to the staternent
Syntax
continue
In a while loop, the next iteration starts by re-evaluating the controlling expression of the while statement. In a for loop, the loop execution clause is executed.
e.g. for i in range (0.3):
print(“Before the continue”)
continue
print(“After the continue, should never print”)
print(“After the for loop”)