Relational Operators

4.2. Relational Operators#

  • A relational operator converts an expression into a boolean type, which is a basic Python data type.

  • Assume a=1 and b=1

Relational Operators

What it does?

Example

==

True if a has the same value as b

a == b (True)

!=

True if a does not have the same value as b

a != b (False)

>

True if a is greater than b

a > b (False)

<

True if a is less than b

a < b (False)

>=

True if a is greater than or equal to b

a >= b (True)

<=

True if a is less than or equal to b

a <= b (True)

  • These operators evaluate to True or False depending on the values you give them.

  • Conditionals are used to instruct computer to make a decision.

45 > 34
45 > 79
45 < 79
45 < 34

23.1 >= 23
23.1 >= 23.1
23.1 <= 23.1
23.1 <= 23

67.3 == 87
67.3 == 67
67.0 == 67
67.0 != 67
67.0 != 23

4.2.1. Combining Comparisons#

x = 2
y = 5
z = 7
x < y and y < z

(x < y) and (y < z) # better


x = 3
(1 < x) and (x <= 5)

x = 7
(1 < x) and (x <= 5)

- Chain comparison allows you to combine multiple comparisons
x = 3 
1 < x <= 5 # You can chain comparisons

3 < 5 != True 
(3 < 5) and (5 != True)

3 < 5 != False
(3 < 5) and (5 != False)

4.2.2. Short-Circuit Evaluation#

  • When Python evaluates an expression containing and or or, it does so from left to right. As soon as it knows enough to stop evaluating, it stops, even if some operands have not been looked at yet. This is called short-circuit evaluation.

  • For and operation, if the first expression is false, the second expression is not evaluated.

  • For or operation, if the first expression is true, the second expression is not evaluated.

is_superuser = True
is_staff = True
is_active = False
if is_superuser or (is_staff and is_active):
    print('Enter!')
else:
    print('You Shall Not Pass!')

is_staff = True
is_active = True
if is_staff and is_active:
    print('Enter!')
else:
    print('You Shall Not Pass!')
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