Practice

Boolean Logic

Comparisons

Let’s practice using our comparison operators. Remember:

Operator Means
< less-than
<= less-than-or-equal-to
> greater-than
>= greater-than-or-equal-to
== equals
!= not-equals

Remember, the first six operators test the object’s value. is and is not test whether two objects are the same thing. This is useful for singletons, such as None or False. We won’t be using them much in this intro course, but feel free to play with them.

>>> 10 > 5
>>> 5 > 10
>>> 10 > 10
>>> 10 >= 10
>>> 5 < 10
>>> 5 < 5
>>> 5 <= 5
>>> 5 == 5
>>> 5 != 10
Here's what you should have seen in your REPL:

Truthiness

Different languages have different ideas of what is “truthy” and “falsy.” In Python, all objects can be tested for truth, and an object is considered True unless except under certain circumstances that we talked about earlier in the chapter. Remember that checking if an object is “equal” to another object doesn’t necessarily mean the same thing. An object is considered “truthy” if it satisfies the check performed by if or while statements.

Let’s try a few of these out:

>>> 5 == True
>>> # The number 5 does not equal True, but...
>>> if 5:
...     print("The number 5 is truthy!")
...
>>> # The number 5 is truthy for an if test!

True and False can also be represented by 1 and 0

>>> 1 == True
>>> 0 == False
Here's what you should have seen in your REPL:

Boolean Operators

Python also supports boolean operators, although they’re a little different than the comparison operators. Remember that or and and return one of their operands, rather than True or False.

Operation Result
x or y if x is false, then y, else x
x and y if x is false, then x, else y
not x if x is false, then True, else False 
>>> True or False
>>> [] or [1, 2, 3]
>>> "Hello" or None

>>> True and False
>>> 5 and 0
>>> [1] and [1, 2, 3]
>>> "Hello" and None

# Of course, you can use `and` and `or` aren't limited to two operands
>>> a = False
>>> b = False
>>> c = False
>>> a or b or c
>>> b = True
>>> a or b or c

>>> a and b and c
>>> a = True
>>> c = True
>>> a and b and c
Here's what you should have seen in your REPL: