Conditionals are control structures that allow a program to make decisions based on certain conditions.
These statements allow us to evaluate expressions and execute different blocks of code depending on whether these expressions are true or false.
In Python, conditionals are primarily implemented through the if
, elif
(short for “else if”), and else
statements.
If you want to learn more about Conditionals
consult the Introduction to Programming Course read more
if
Statement
The if
statement is used to execute a block of code if a condition is true. The basic syntax is as follows:
if condition:
# block of code if the condition is true
For example, we can use an if
to check if a number is greater than 10:
number = 15
if number > 10:
print("The number is greater than 10")
In this case, since the condition number > 10
is true, the print
will execute and we will see “The number is greater than 10” in the output.
else
Statement
The else
statement is used to execute a block of code when the condition in the if
is false. The syntax is as follows:
if condition:
# block of code if the condition is true
else:
# block of code if the condition is false
Following the previous example, we could add an else
to handle the case where the number is not greater than 10:
number = 5
if number > 10:
print("The number is greater than 10")
else:
print("The number is less than or equal to 10")
In this case, since number
is 5 and the condition number > 10
is false, the block of code inside the else
will execute and we will see “The number is less than or equal to 10” in the output.
elif
Statement
The elif
statement is used to evaluate multiple conditions sequentially. It is short for “else if”.
The syntax is as follows:
if condition_1:
# block of code if condition_1 is true
elif condition_2:
# block of code if condition_1 is false and condition_2 is true
else:
# block of code if all previous conditions are false
Let’s see an example where we use elif
to classify a number in relation to 0:
number = 5
if number > 0:
print("The number is positive")
elif number < 0:
print("The number is negative")
else:
print("The number is zero")
In this case, since number
is 5 and is greater than 0, the first block of code will execute and we will see “The number is positive” in the output.
Multiple Conditions
It is also possible to combine multiple conditions using the and
, or
, and not
operators. These operators allow us to construct more complex conditions:
and
: ReturnsTrue
if both conditions are true.or
: ReturnsTrue
if at least one of the conditions is true.not
: ReturnsTrue
if the condition is false.
For example:
x = 10
y = 5
z = 0
if x > y and y > z:
print("All conditions are true")
In this case, all three conditions are true (x > y
, y > z
, and x > z
), therefore, the print
will execute.