Conditional Statements in
Python
What are Decision Making statements in Python?
What
are branching statements in Python?
Conditional statements or decision making statements
are statements used to evaluate a particular expression based on test condition
result. The test condition result is true or false. If test condition becomes
true then particular block is executed and if test condition becomes false then
particular block get execute.
For example
If you want to evaluate student is pass or fail in
examination based on percentage of student. Then you can write test condition
on percentage as follows,
percentage >=40
“Student is Pass” else “student
is fail”. This kind of decision making problems are solved with the help of
conditional statements.
Types
of Conditional statements in Python
1. if
statement:
The if statement is used to execute block of code if
test condition becomes true.
General syntax of if statement:
if test_condition:
statement
In above syntax
if keyword is used to to write if statement. Test condition is the test
expression which is used to test the particular condition. Test condition follows
by the colon. After colon indentation is followed to write code block for if
statement.
a=110
if a==110:
print("A is 110")
Output:
A is 110
Here value of a is initialized as 110. Test condition
is applied on a to compare a with 110. i.e. if value of a is exactly equals to
110 then if block will get execute. If test condition becomes false then nothing
will get execute. In above example test condition becomes true so if block
executed and result displayed on screen.
2. If-else
Statement:
If else statement is used to
evaluate a particular code block based on test condition result i.e. true or
false. If test condition result is true then if code block executes and if test
condition becomes false then else code block executes. In if else statement if
and else keywords are used. For both if and else statement the indentation is
followed to represent the code block.
General syntax of if else
statement,
if test_expression:
code block to be executed if test condition becomes true
else:
code block to be executed if test condition becomes false
For example,
a=111
if a==110:
print("A is 110")
else:
print("A is not 110")
Output:
A is not 110
In above example value of a is
111. A is compare with 110 by using equality operator. Here test condition
becomes false because value of a is 111 and it is compared with 110. It is not
exactly equals to 110. So if code block is not executed. Else block executed
and output is A is not 110.
3. if-elif-else
statement:
if-elif=else statement is used to test multiple
conditions and based on test condition result if true the particular code block
is executed.
General syntax
if testcondition1:
code
block is executed if testcondition1 is true
elif testcondition2:
code
block is executed if testcondition2 is true
elif testcondition3:
code
block is executed if testcondition3 is true
else:
code
block is executed if testcondition3 is false
Here testcondition1 is checked. If testcondition1
result is true, the code block is executed. If test condition1 becomes becomes
false the control goes to test the test
condition2. If testcondition2 result is true then this code block is executed
otherwise compiler goes to test the testcondition3. Here again if testcondition3
becomes false then the default statement i.e. else block get executed.
For example,
a=10
b=100
if (a>b):
print("A is bigger")
elif a<b:
print("A is smaller")
else:
print("Both numbers are equals")
Output:
A is smaller
In above example valueof a and b are 10 and 100
respectively. A is compared with b to check a is greater then b or not. If test
condition becomes true then if code block is executed. If test condition
becomes false then compiler goes to next test condition which is written with
elif to test a is smaller than b. Here test condition becomes true so code
block written in elif block is executed. The if-elif-else statement is very
useful in case of multiple conditions. The elif is nothing but else-if and we can use
multiple elif statements to test multiple test conditions.
4. Nested
if statement:
The nested if statement is a if statement in Python
which is written in another if statement. Nested if statement is used to test more
than one test and based on test condition execute the statement.
General syntax:
if testcondition1:
statement
to be executed if condition1 is true
if testcondition2:
statement
to be executed if condition2 is true
else:
statement
to be executed if testcondition2 is false
else:
statement
to be executed if testcondition1 is false
In the syntax statement written in testcondition1 is
executed if test condition1 is true. The compiler will check one another test
condition written inside the other test condition i.e. testcondion1. If test
condition2 is true compiler will evaluate statement written in test condition2.
If test condition2 becomes false then code in side outer if get executed. If
test condition1 becomes false then outer else code block get execute.
For example,
a=7
if a>0:
print("A positive number")
if a%2==0:
print("a is even number")
else:
print("a is odd number")
else:
print("A is negative number")
Output:
A positive number
a is odd number
In this example first a is compare with 0. If a is
greater than 0 this condition is true then compiler will execute outer if code
block and then control goes to check inside if block. Here a is divided by to
and remainder is calculated. If remainder is exactly equals to 0 then inside if
block get execute, if this condition becomes false then inside else block get
execute. But if initially test condition1 i.e. outer if condition becomes false
then compiler will execute outer else code block.
In this example outer if test condition is true so a
is positive is displayed and then second condition is checked, here test condition
becomes false so inner else code block i.e. number is odd is displayed.
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