Skip to main content

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 Unv, and get one of two answers, true or false.

When you compare two values, the expression is evaluated and Unv returns the Boolean answer:

print(10  >  9)  
print(10  ==  9)  
print(10  <  9)

When you run a condition in an if statement, Unv 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")

Evaluate Values and Variables​

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))

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.

The following will return True:

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.

The following will return False:

bool(False)  
bool(None)  
bool(0)  
bool("")  
bool(())  
bool([])  
bool({})

Functions can Return a Boolean​

You can create functions that returns a Boolean Value:

Print the answer of a function:

function  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!":

function  myFunction()
    return  true  
  
if  myFunction()
    print("YES!")  
else
    print("NO!")

Exercises​

The statement below would print a Boolean value, which one?

print(10 > 9)
Supported Runtimes

Check is your flavour of Unv is supported.