Learn Python / Booleans and Comparisons

Booleans and Comparisons

Programs constantly ask yes-or-no questions: Is the password correct? Is the user old enough? Is the cart empty? In Python, the answer to such a question is a boolean: either True or False.

True and False

True and False are values of type bool. Note the capital letters.

is_raining = True
has_umbrella = False

print(is_raining)
print(type(has_umbrella))
Output


Comparison operators


Comparison operators compare two values and give back True or False:






Operator
Meaning
Example
Result






==
Equal to
5 == 5
True




!=
Not equal to
5 != 3
True




<
Less than
3 < 5
True




>
Greater than
3 > 5
False




<=
Less than or equal to
5 <= 5
True




>=
Greater than or equal to
4 >= 5
False






age = 17

print(age == 18)
print(age != 18)
print(age < 18)
print(age >= 18)
Output




Watch out: = assigns a value, while == compares two values. Mixing them up is one of the most common beginner mistakes.




You can store the result of a comparison in a variable:


age = 20
is_adult = age >= 18
print(is_adult)
Output


Chaining comparisons


Python lets you chain comparisons the way you would in maths:


temperature = 22

print(18 <= temperature <= 25)   # is it between 18 and 25?
print(0 < temperature < 10)
Output


Comparing strings


Strings can be compared too. == checks for an exact match, and it's case-sensitive:


print("python" == "python")
print("Python" == "python")
print("python" == "Python".lower())
Output


 Going deeper: Comparing text with < and > optional
< and > compare strings alphabetically, character by character. One surprise: all capital letters come before all lowercase letters, so "Zebra" comes before "apple":


print("apple" < "banana")
print("cat" > "car")
print("Zebra" < "apple")
Output


Convert both sides with .lower() first if you want a true alphabetical comparison.


 Going deeper: Comparing decimal numbers optional
Because floats aren't always exact (remember 0.1 + 0.2 from the Numbers and Math lesson?), comparing them with == can surprise you. The math module has isclose(), which checks whether two numbers are close enough:


import math

print(0.1 + 0.2 == 0.3)
print(math.isclose(0.1 + 0.2, 0.3))
Output


Logical operators: and, or, not


Combine several conditions with and, or and not:


    

  • a and b is True only if both are True.
    • 

  • a or b is True if at least one is True.
    • 

  • not a flips True to False and back.
    • 



age = 25
has_ticket = True

print(age >= 18 and has_ticket)   # both true
print(age < 12 or age > 65)       # neither is true
print(not has_ticket)
Output


Here's how they work for every combination:






a
b
a and b
a or b
not a






True
True
True
True
False




True
False
False
True
False




False
True
False
True
True




False
False
False
False
True






When you mix them, not is applied first, then and, then or. Use parentheses to make longer conditions easy to read:


is_weekend = True
is_holiday = False
is_raining = True

go_to_park = (is_weekend or is_holiday) and not is_raining
print(go_to_park)
Output


Truthiness


Python can treat any value as true or false. Use bool() to see how a value is treated:


print(bool(0))       # False
print(bool(42))      # True
print(bool(""))      # False: empty string
print(bool("hi"))    # True
print(bool(None))    # False
print(bool(0.0))     # False
Output


The rule is simple. Zero, empty values and None are "falsy", which just means Python treats them like False. Almost everything else is "truthy", treated like True. This becomes very handy with if statements in the next lesson.


 Going deeper: Booleans are numbers too optional
Under the hood, True behaves like 1 and False like 0. That lets you count how many conditions are true by adding them up:


passed_math = True
passed_science = False
passed_english = True

print(passed_math + passed_science + passed_english)
Output


 Going deeper: Checking for None with is optional
To check whether a variable holds None, Python programmers write is None rather than == None:


result = None

print(result is None)
print(result is not None)
Output


== asks "do these have the same value?", while is asks "are these the very same object?". There's only ever one None, so is is the precise way to check for it. You'll see is None in later lessons, for example in Function Arguments.


Use is only for None. For numbers, strings and everything else, compare values with ==.


Exercises


Exercise 1: Voting age


Print True if age is 18 or over, otherwise False. Try changing age to check both cases.


age = 16

Output





Exercise 2: In range


Print True if score is between 0 and 100 (inclusive). Use a chained comparison.


score = 87

Output





Exercise 3: Login check


A login succeeds when the username is "admin" and the password is "secret123". Print whether the login succeeds. The username check should ignore capital letters.


username = "Admin"
password = "secret123"

Output






Exercise 4: Predict the output


Before you run this, predict what each line prints. Then run it to check.


print(10 > 5 and 3 > 7)
print(10 > 5 or 3 > 7)
print(not 10 > 5)
print(bool("False"))
print("abc" == "ABC".lower())
Output





Summary


    

  • A boolean is True or False, and its type is bool.
    • 

  • Comparison operators ==, !=, <, >, <= and >= produce booleans. Don't confuse == with =.
    • 

  • Comparisons can be chained: 0 <= x <= 100.
    • 

  • and, or and not combine conditions. Use parentheses for clarity.
    • 

  • Zero, empty strings and None are falsy. Most other values are truthy.
    •