Python If ... Else Statements: Logical Conditions and Syntax

Understand how to use if and else statements in Python to control the flow of your code based on logical conditions. Learn about various comparison operators such as equals, not equals, less than, and greater than, and see how these are used in conditional statements and loops.

Python If ... Else

Python supports the usual logical conditions from mathematics:

  • Equals: a == b
  • Not Equals: a != b
  • Less than: a < b
  • Less than or equal to: a <= b
  • Greater than: a > b
  • Greater than or equal to: a >= b

These conditions are used in "if statements" and loops. An "if statement" is written using the if keyword.

If Statement

Example

a = 20
b = 30
if b > a:
  print("b is greater than a")
Output

b is greater than a

Indentation

Python relies on indentation (whitespace at the beginning of a line) to define scope in the code.

Example (Incorrect Indentation)

a = 20
b = 30
if b > a:
print("b is greater than a")  # This will raise an error

Elif Statement

The elif keyword is Python's way of saying "if the previous conditions were not true, then try this condition".

Example

a = 25
b = 25
if b > a:
  print("b is greater than a")
elif a == b:
  print("a and b are equal")
Output

a and b are equal

Else Statement

The else keyword catches anything which isn't caught by the preceding conditions.

Example

a = 30
b = 20
if b > a:
  print("b is greater than a")
elif a == b:
  print("a and b are equal")
else:
  print("a is greater than b")
Output

a is greater than b

Short Hand If

If you have only one statement to execute, you can put it on the same line as the if statement.

Example

a = 50
b = 30
if a > b: print("a is greater than b")
Output

a is greater than b

Short Hand If ... Else

If you have only one statement to execute for each condition, you can put it all on the same line:

Example

a = 10
b = 50
print("A") if a > b else print("B")
Output

B

Multiple Conditions

Example

a = 50
b = 50
print("A") if a > b else print("=") if a == b else print("B")
Output

=

Logical Operators

Use logical operators to combine conditional statements:

And

Example

a = 60
b = 40
c = 100
if a > b and c > a:
  print("Both conditions are True")
Output

Both conditions are True

Or

Example

a = 70
b = 20
c = 50
if a > b or a > c:
  print("At least one of the conditions is True")
Output

At least one of the conditions is True

Not

Example

a = 25
b = 75
if not a > b:
  print("a is NOT greater than b")
Output

a is NOT greater than b

Nested If Statements

You can have if statements inside if statements, this is called nested if statements.

Example

x = 45
if x > 10:
  print("Above ten,")
  if x > 20:
    print("and also above 20!")
  else:
    print("but not above 20.")
Output

Above ten,
and also above 20!

The pass Statement

If you have an if statement with no content, put in the pass statement to avoid an error.

Example

a = 30
b = 60
if b > a:
  pass