Python: How to Use if-then-else Statements
Posted in Python by Dirk - last update: Dec 19, 2023
In programming, if-then-else statements are used for conditional execution, allowing you to control the flow of your program based on certain conditions. Python has multiple ways to handle this, from a simple if
statement to complex nested if
statements
Simple if statement
This is the most basic form of the if
statement. It checks a condition, and if it evaluates to True
, the indented block of code beneath it is executed.
if condition:
# Code to be executed if the condition is True
if - else statement
In this form, if the condition is True
, the code inside the first block is executed; otherwise, the code inside the second block (after else
) is executed.
if condition:
# Code to be executed if the condition is True
else:
# Code to be executed if the condition is False
if - elif - else statement
This allows you to check multiple conditions in sequence. If the first condition is True
, the corresponding block of code is executed. If not, it checks the next condition (elif
stands for else if
).
If none of the conditions are True, the code in the else block is executed.
if condition1:
# Code to be executed if condition1 is True
elif condition2:
# Code to be executed if condition2 is True
else:
# Code to be executed if none of the conditions are True
Nested if statements:
You can also nest if statements within each other to create more complex conditional structures.
if condition1:
# Code to be executed if condition1 is True
if condition2:
# Code to be executed if both condition1 and condition2 are True
else:
# Code to be executed if condition1 is True but condition2 is False
else:
# Code to be executed if condition1 is False
Shorthand if else statements
Python also supports a one-liner conditional expression, also known as the ternary operator or . It provides a concise way to write simple if-else statements.
result = value_if_true if condition else value_if_false
Logical operators
Logical operators are used to combine multiple conditions in Python’s if statements to create more complex conditions. Here are some examples using logical operators:
and operator
The and
’ operator requires both conditions to be True
for the combined condition to be True
.
age = 25
income = 50000
if age > 18 and income > 30000:
print("Eligible for a loan")
else:
print("Not eligible for a loan")
In the example above - both conditions (age above 25 and income above 50.000) need to be fulfilled to get a loan.
or operator
The or
operator requires at least one of the conditions to be True for the combined condition to be True
.
is_student = True
is_employee = False
if is_student or is_employee:
print("You are part of the academic community.")
else:
print("You are not part of the academic community.")
In the example above - one can be or student or employee of the academic community at the university.
not operator
The not
operator negates the condition, making True conditions False and vice versa.
has_permission = False
if not has_permission:
print("Access denied.")
else:
print("Access granted.")
In the example above - if you don’t have a permission - access is denied.
Combining multiple conditions
You can use logical operators to combine more than two conditions.
is_weekend = True
has_time_off = True
is_sunny = False
if is_weekend and has_time_off and not is_sunny:
print("Let's have a relaxing indoor weekend.")
else:
print("Plan your activities accordingly.")
In this example - you plan an indoor weekend when it is weekend, you are free, and it is not sunny.
References:
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