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5 Decision Making in Python

Pre-Processing
Pre-Processing
• Conditional Statements • If Statement
• If … Else Statement • Nested If … Else Statement
• If … Elif … Else Ladder • Indentation of Statements in Python

The statements in a program are usually executed in sequence.
But, sometimes we may need to decide between two courses Start
of actions, depending on a specific situation that arises during Input Number Test Condi on 1 No
Is
the execution of the program. Decision making is the process of N True?
evaluating a given condition and deciding the course of action
to follow based on the result of the condition. Is No Yes
N > 0 ?
Consider the example of accepting a number from the user and
Is
Execute
deciding whether the number is positive or negative. We know Yes No Test Condi on 1 else block
that a number is positive if it is greater than or equal to 0, else Print N is Print N is True?
it is negative. Thus, we need to check the condition to see if the Posi ve Nega ve
variable containing the number is greater than 0 or not. Stop Yes

The flow chart given in the image illustrates the decision-making Start Execute
if block
involved in the process of checking whether a number is positive or not. Is
Input Number Test Condi on 1 No
CONDITIONAL STATEMENTS N True?
The statements that let us take decisions in a Python program are called Conditional statements. Yes
Is
Is
These statements work on the basis of specific conditions. Test Condi on Yes No Execute
N > 0 ?
if block
True?
Is
Python provides several decision-making statements. Let us learn about them. Test Condi on 1 Yes Execute
Is
if block 3
Yes No Test Condi on 1 Execute
True?
IF STATEMENT No Print N is True? else block
Print N is
Nega ve
Posi ve
The if statement is the simplest conditional statement. It evaluates a test condition. If the test No
condition evaluates to True, the block of statements under if is executed. If the test condition Yes
Stop
evaluates to False, the block of statements under if is bypassed and the control is passed to the Execute
Is
if block
Execute
Execute
statement after the if block. if block 3 Yes Test Condi on 2 Yes if block 3
True?
The statement used with the if statement is called Selection statements.
The syntax for using the if statement is: No
Is
if <test condition>: Test Condi on Yes Execute
Is
True?
Test Condi on Yes Execute if block Is Is
set of statements True? if block Test Condi on 3 Yes Execute
Test Condi on 1
True?
True? if block 3
other statements No
No
No No
Execute 43
else block
Execute
Is
Execute Yes else block Yes Execute
if block 3 Test Condi on 2 if block 3
True?
No
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Is
Test Condi on Yes Execute Is
if block
True? Test Condi on 3
True?
No
No
Execute
else block
Execute
else block

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