if conditional statement

The if conditional statement allows us to check if a given condition is fulfilled. We commonly use logical operators in conditional statements.

x = int(input())
if x == 5:
    print("The user entered the number 5.")
                                    

We use the modulo operator very often in conditional statements. In the example below, the condition checks if the x variable is divisible by 2 (whether it is even).

x = int(input())
if x % 2 == 0:
    print("The user entered an even number.")
                                    

We can simplify the if statement by using boolean conditions. We can just write if x:, and if x is True, the instruction will be executed. True means any value other than 0.

else and elif conditional statements

else is a statement that allows us to simplify our code by avoiding the need for another if statement, replacing it with an alternative action when the original condition is False.

x = int(input())
if x > 0:
    print("The user entered a positive number.")
else:
    print("The user entered a negative number.")
                                    

The code above doesn't handle the case where the user enters 0. To do that, we need elif (else + if). It works similarly to else, but allows us to specify an additional condition (like in an if statement). We can use as many elif instructions as we want, relating to a single if.

x = int(input())
if x > 0:
    print("The user entered a positive number.")
elif x < 0:
    print("The user entered a negative number.")
else:
    print("The user entered 0.")
                                    

We use this instruction instead of writing multiple if statements because if any of the conditions relating to a single if statement have been met, the rest will not be considered.

break and continue keywords

The break keyword is used to break the continuity of a loop, and continue can skip particular iterations within it.

while True:
    x = int(input())
    if x > 0:
        break
        
for x in range(10):
    if x == 4 or x == 8:
        continue
    print(x)
                                    

else in loops

else also works with loops, but on different principles. The else block that follows the loop won't be executed only if there is a break statement inside the loop. This structure is unique to Python, and we shouldn't use it very often because it can be confusing.

x = 3
while x > 4:
    x -= 1
    print("Loop")
else:
    print("Else")
print("Outside")
                                    

x = 6
while x > 4:
    x -= 1
    print("Loop")
else:
    print("Else")
print("Outside")
                                    

x = 10
while x > 4:
    x -= 1
    print("Loop")
    if x == 7:
        break
else:
    print("Else")
print("Outside")
                                    

for x in range(5):
    print("Loop")
else:
    print("Else")
print("Outside")
                                    

for x in range(5):
    print("Loop")
    if x == 2:
        break
else:
    print("Else")
print("Outside")
                                    

match conditional statement (switch)

match is an instruction that simplifies complex conditions by replacing multiple if and elif statements with a more concise structure.

x = int(input())

match x:
    case 0:
        print("x equals 0")
    case 25:
        print("x equals 25")
    case 50:
        print("x equals 50")
    case _: # the default case
        print("x doesn't equal 0, 25, or 50")
                                    

A parameter of the match statement is usually an integer or a string (but it could be something else).

Ternary operations

A ternary operation is a simplifed one-line version of the if-else statement.

x, y = 1, 2 # defining variables in bulk
z = x if x < y else y
print("The smaller numer is:", z)
                                    

The walrus operator

The walrus operator := allows us to assign a value to a variable as part of an expression. It can make code more concise by combining assignment and condition checks in a single line.

numbers = [1, 2, 3, 4, 5]
total = 0

while (n := len(numbers)) > 0:
    total += numbers.pop()
    print("Popped number, remaining count:", n)

print("Total sum:", total)