Python Booleans
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:
When you run a condition in an if statement, Python returns
True or False:
Example
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")
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Evaluate Values and Variables
The bool() function allows you to evaluate
any value, and give you
True or False
in return,
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.
Example
The following will return True:
bool("abc")
bool(123)
bool(["apple", "cherry", "banana"])
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Some Values are False
In fact, there are not many values that evaluates to
False, except empty values, such as (),
[], {},
"", the number
0, and the value None.
And of course the value False evaluates to
False.
Example
The following will return False:
bool(False)
bool(None)
bool(0)
bool("")
bool(())
bool([])
bool({})
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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))
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Functions can Return a Boolean
You can create functions that returns a Boolean Value:
Example
Print the answer of a function:
def myFunction() :
return True
print(myFunction())
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You can execute code based on the Boolean answer of a function:
Example
Print "YES!" if the function returns True, otherwise print "NO!":
def myFunction() :
return True
if myFunction():
print("YES!")
else:
print("NO!")
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Python also has many built-in functions that returns a boolean value, like the
isinstance()
function, which can be used to determine if an object is of a certain data type:
