Booleans represent one of two values: True or False .
Boolean Values
In programming you often need to know if an expression is True or False .
You can evaluate any expression in Python, and get one of two answers, True or False .
When you compare two values, the expression is evaluated and Python returns the Boolean answer:
Example
print(10 > 9)
print(10 == 9)
print(10 < 9)When you run a condition in an if statement, Python returns True or False :
TrueEvaluate Values and Variables
The bool() function allows you to evaluate any value, and give you True or False in return,
Example
print(bool("Hello"))
print(bool(15))Example
x = "Hello"
y = 15
print(bool(x))
print(bool(y))Most Values are True
Almost any value is evaluated to True if it has some sort of content.
Any string is True , except empty strings.
Any number is True , except 0 .
Any list, tuple, set, and dictionary are True , except empty ones.
bool("abc")
bool(123)
bool(["apple", "cherry", "banana"])Some Values are False
In fact, there are not many values that evaluate to False , except empty values, such as () , [] , {} , "" , the number 0 , and the value None . And of course the value False evaluates to False .
bool(False)
bool(None)
bool(0)
bool("")
bool(())
bool([])
bool({})One more value, or object in this case, evaluates to False , and that is if you have an object that is made from a class with a len function that returns 0 or False :
Example
class myclass():
def __len__(self):
return 0
myobj = myclass()
print(bool(myobj))Functions can Return a Boolean
You can create functions that returns a Boolean Value:
Example
def myFunction() :
return True
print(myFunction())You can execute code based on the Boolean answer of a function:
Example
def myFunction() :
return True
if myFunction():
print("YES!")
else:
print("NO!")Python also has many built-in functions that return a boolean value, like the isinstance() function, which can be used to determine if an object is of a certain data type:
Example
x = 200
print(isinstance(x, int))