Understanding Python Conditional Statements: If, Else, and Elif

Conditional statements in Python allow programs to make decisions based on certain conditions. Python provides several logical operators commonly used in mathematics to compare values:

• 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

Basic If Statement

The if keyword initiates a conditional block. Here’s an example:

a = 33
b = 200

if b > a:
    print("b is greater than a")

In this case, since 200 is greater than 33, the condition is true and the message is printed.

Indentation in Python

Python uses indentation to define blocks of code. Unlike other programming languages that use braces, Python relies on whitespace to determine scope. Incorrect indentation leads to syntax errors:

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

Using Elif

elif (short for “else if”) allows additional conditions to be checked if the initial if is false.

a = 33
b = 33

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

Using Else

The else block executes if none of the preceding conditions are true:

a = 200
b = 33

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")

Else Without Elif

else can also be used independently when no elif is necessary:

if b > a:
    print("b is greater than a")
else:
    print("b is not greater than a")

Short-Hand If

Python supports a short-hand version of the if statement for single-line execution:

if a > b: print("a is greater than b")

Short-Hand If…Else (Ternary Operator)

You can use a one-line if...else expression, known as a ternary operator:

a = 2
b = 330

print("A") if a > b else print("B")

Multiple conditions can also be nested in a single line:

a = 330
b = 330

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

Logical Operators

And Operator

The and keyword checks if both conditions are true:

a = 200
b = 33
c = 500

if a > b and c > a:
    print("Both conditions are True")

Or Operator

The or keyword checks if at least one condition is true:

if a > b or a > c:
    print("At least one of the conditions is True")

Not Operator

The not keyword reverses the result of a condition:

a = 33
b = 200

if not a > b:
    print("a is NOT greater than b")

Nested If Statements

Python supports nesting of if statements within each other:

x = 41

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

The Pass Statement

When you want to define an if block with no action (as a placeholder), use the pass keyword:

a = 33
b = 200

if b > a:
    pass

Learn More with Devyra

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