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Booleans represent one of two values: True or False
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:
print(10 > 9)
print(10 == 9)
print(10 < 9)
When you run a condition in an if statement, Python returns
True
or False
:
Print a message based on whether the condition is True
or
False
:
a = 200
b = 33
if b > a:
print("b is greater than a")
else:
print("b is not greater than a")
The bool()
function allows you to evaluate
any value, and give you
True
or False
in return,
Evaluate a string and a number:
print(bool("Hello"))
print(bool(15))
Evaluate two variables:
x = "Hello"
y = 15
print(bool(x))
print(bool(y))
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.
The following will return True:
bool("abc")
bool(123)
bool(["apple", "cherry", "banana"])
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
.
The following will return 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
:
class myclass():
def __len__(self):
return 0
myobj = myclass()
print(bool(myobj))
You can create functions that returns a Boolean Value:
Print the answer of a function:
def myFunction() :
return True
print(myFunction())
You can execute code based on the Boolean answer of a function:
Print "YES!" if the function returns True, otherwise print "NO!":
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:
Check if an object is an integer or not:
x = 200
print(isinstance(x, int))
The statement below would print a Boolean value, which one?
print(10 > 9)