# Python – Decision Making

Conditional Statements

An if statement in python takes an expression with it. If the expression amounts to True, then the block of statements under it is executed. If it amounts to False, then the block is skipped and control transfers to the statements after the block.

Syntax:

```if condition:
# Statements to execute if
# condition is true```

Here, condition after evaluation will be either true or false. if statement accepts boolean values – if the value is true then it will execute the block of statements below it otherwise not. We can use condition with bracket ‘(‘ ‘)’ also.

```if condition:
statement1
statement2

# Here if the condition is true, if block
# will consider only statement1 to be inside
# its block.```
```python program to illustrate If statement
i = 10
if (i > 15):
print ("10 is less than 15")
print ("I am Not in if")```

Output:

`I am Not in if`

if- else

If…else statements: The else statement block is executed if the logical expression defined in if statement returns a FALSE value.

Syntax:

```if (condition):
# Executes this block if
# condition is true
else:
# Executes this block if
# condition is false```
```python program to illustrate If else statement
!/usr/bin/python

i = 20;
if (i < 15):
print ("i is smaller than 15")
print ("i'm in if Block")
else:
print ("i is greater than 15")
print ("i'm in else Block")
print ("i'm not in if and not in else Block")

Output:
i is greater than 15
i'm in else Block
i'm not in if and not in else Block```

nested-if

If another condition has to be checked after a certain condition then nested if statements can be used. In a nested, if construct, the if…elif…else construct is used to execute statements based on multiple conditions.

Syntax:

```if (condition1):
# Executes when condition1 is true
if (condition2):
# Executes when condition2 is true
# if Block is end here
# if Block is end here```
```python program to illustrate nested If statement
!/usr/bin/python

i = 10
if (i == 10):
#First if statement
if (i < 15):
print ("i is smaller than 15")
#Nested - if statement
#Will only be executed if statement above
#it is true
if (i < 12):
print ("i is smaller than 12 too")
else:
print ("i is greater than 15")

Output:
i is smaller than 15
i is smaller than 12 too```

Here, a user can decide among multiple options. The if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.

Syntax:-

```if (condition):
statement
elif (condition):
statement
.
.
else:
statement```
```i = 20
if (i == 10):
print ("i is 10")
elif (i == 15):
print ("i is 15")
elif (i == 20):
print ("i is 20")
else:
print ("i is not present")```

Output:
i is 20