Logical Operators¶
The three logical operators in Python are and, or, and not. They are used to combine
the True or False values of variables or expressions into a result that is
either True or False. Let’s look at some examples.
Create a Jupyter Notebook and name it intro_logical_operators and follow along.
and operator¶
x = 5
print(x > 3 and x < 10) # both are True so result is True
True
print(x > 3 and x < 0) # one is True and other is False so result is False
False
print(x < 0 and x > 3) # one is False and other is True so result is False
False
print(x < 0 and x > 3) # one is False and other is True so result is False
False
print(x < 0 and x < 3) # both are False so result is False
False
The above examples were with numbers but the logical operators
can be used with any valid Python expressions that are either
True or False. For the and operator, the result is
only True if both things are True. If there is at least one
False then the result is False. This should be clear from
the English Language. If someone said you could have a cookie
if you cleaned your room and cleaned the dishes, then you
would know you would have to do both things to get the cookie.
True and True
True
True and False
False
False and True
False
False and False
False
You can chain multiple logical operators together.
And it is often wise to use () to keep things clear.
For example,
('hello' == 'hello') and (5 != 6) and (5 > -1) and ('A' != 0) # True and True and True and True is True
True
('hello' == 'hellooo') and (5 != 6) and (5 > -1) and ('A' != 0) # False and True and True and True is False
False
When chaining multiple ands together, the result is True if all the intermediate results are True. If there is at least one False then the final result is False.
or operator¶
With the or operator, the resulting expression is True if there is at least
one True. Otherwise it is False.
True or False
True
False or True
True
True or True
True
False or False
False
a = 'cat'
b = 'dog'
c = a
a == b or c == a # False or True is True
True
c == a or a == b # True or False is True
True
(5 == 5) or ( 0 > 1) or ( 5 == 4) or (10 > -5) or (10 != 10) # at least one is True so result is True
True
not operator¶
The not operator takes any expression that is True or False and
simply flips it to the opposite.
not True
False
not False
True
not (1 == 1)
False
not (5 < 4)
True
not (-4 < -4)
True
not ('hello' == 'hello')
False
Simple Practice Using Operators¶
We will be using these comparison and logical operators a lot. Take some time now to understand
what each means and their differences. All of the expressions below will evaluate to either True or False.
Try them first before checking in python. Make sure you understand why each one
is either True or False. These are all examples of boolean expressions. Boolean expressions
are expressions which evaluate to either True or False.
5 == 5
5 >= 5
5 <= 5
5 < 6
'4' + '3' == 7
str(10) + str(10) == '1010'
'a' + 'b' == 'a b'
5 + int('123') == 5123
str(5) + '5' == '55'
(5 > 3) and (5 > 4)
(5 > 3) and (4 < 5)
(5 > 3) or (5 > 4)
(2 < 1) or (3 < 1)
1 == 1
not (1 == 1)
5 > 3 or 3 < 5
not (5 > 3 or 3 < 5)
(not 3 == 5) and not (4 == 4)
not ( (True or False) and (False and True) )
not (True or False) == (not True) and (not False)
not (True and True) == (not True) or (not True)