Conditionals

1. The comparison (otherwise known as relational) operators are used to compare values. The table below illustrates how the comparison operators work, assuming that x = 0, y = 1, and z = 0:

Operator Description Example
== returns True if operands’ values are equal, and False otherwise
!= returns True if operands’ values are not equal, and False otherwise
x != y # True
x != z # False
> True if the left operand’s value is greater than the right operand’s value, and False otherwise
x > y # False
y > z # True
< True if the left operand’s value is less than the right operand’s value, and False otherwise
x < y # True
y < z # False
True if the left operand’s value is greater than or equal to the right operand’s value, and False otherwise
x >= y # False
x >= z # True
y >= z # True
True if the left operand’s value is less than or equal to the right operand’s value, and False otherwise
x <= y # True
x <= z # True
y <= z # False

2. When you want to execute some code only if a certain condition is met, you can use a conditional statement:

    • a single if statement, e.g.:
    • a series of if statements, e.g.:

Each if statement is tested separately.

    • an if-else statement, e.g.:
    • a series of if statements followed by an else, e.g.:

Each if is tested separately. The body of else is executed if the last if is False.

    • The if-elif-else statement, e.g.:

If the condition for if is False, the program checks the conditions of the subsequent elif blocks – the first elif block that is True is executed. If all the conditions are False, the else block will be executed.

    • Nested conditional statements, e.g.:

 

 

Exercise 1

What is the output of the following snippet?

x = 5
y = 10
z = 8

print(x > y)
print(y > z)

 

False
True
output

 

Exercise 2

What is the output of the following snippet?

x, y, z = 5, 10, 8

print(x > z)
print((y – 5) == x)

 

False
True
output

 

Exercise 3

What is the output of the following snippet?

x, y, z = 5, 10, 8
x, y, z = z, y, x

print(x > z)
print((y – 5) == x)

 

True
False
output

 

Exercise 4

What is the output of the following snippet?

x = 10

if x == 10:
print(x == 10)
if x > 5:
print(x > 5)
if x < 10:
print(x < 10)
else:
print(“else”)

 

True
True
else
output

Exercise 5What is the output of the following snippet?

x = "1"

if x == 1:
print(“one”)
elif x == “1”:
if int(x) > 1:
print(“two”)
elif int(x) < 1:
print(“three”)
else:
print(“four”)
if int(x) == 1:
print(“five”)
else:
print(“six”)

 

four
five
output

 

Exercise 6

What is the output of the following snippet?

x = 1
y = 1.0
z = "1"

if x == y:
print(“one”)
if y == int(z):
print(“two”)
elif x == y:
print(“three”)
else:
print(“four”)

 

one
two
output