A Truth Table for Python Boolean Expressions Expression 1 Connector Expression 2 Result True and True True False and True False * True and False False False and False False * True or True True * False or True True True or False True * False or False False What Are the Precedence Rules For Python Boolean Expressions? Results marked with a * are those results that are the result of short-circuit expressions. Some students find it helpful to construct a truth table when learning about Boolean values. In this case, we already know that the result is “True”, so the right-hand side is ignored. Therefore, if each of these sides is a function that returns a Boolean result, if the first returns False, the second one will never be executed! For the “ or” keyword, the right-hand side is not evaluated if the left-hand side evaluates to “True”. The Python compiler “knows” that it can’t get a True result for “ and” if the first expression is False, so it skips it. What this means is that for “ and“, if the first expression (on the left side of "and“) is false, the right-hand side is never evaluated. Since one of the expressions is true, changing the “ and” to “ or” in the example above changes the output to “Go out with friends.” On the other hand, if both expressions are false, then the “ else” clause will run either way.īoth “ and” and “ or” are said to be “short-circuit expressions”. If money_available_dollars > 10 and time_available_minutes > 120: Because we’re using “ and” and not “ or“, the compound expression evaluates to false, so the else clause is executed. Advertisements Operator How to Read It x = y x equals y x != y x does not equal y, x is not equal to y x >= y x is greater than or equal to y x = 2.5:Įlif potato_size_inches >= 1.5 and potato_size_inches 120) is true. We’ve seen a lot of this already in our example, but here are the Python comparison operators and what they mean. Another way to describe Boolean expressions in Python (or other languages) is to say that they are expressions that make a comparison. Message = "Hello, world!" Python Comparison Operatorsįrequently, Boolean expressions are expressions that use comparison operators. Note that the double equals of a Boolean expression ( =) are different from the single equals sign that we used to assign a value to a variable: # Assign a string variable to message. # Is the number of characters in the string "Hello" equal to one? For example: # Is three greater than two? It’s possible and acceptable to set a variable to one of these values, but what’s even more common than Boolean variables are Boolean expressions, which are any expression that returns a True or False value. In Python, there are two Boolean constants that are capitalized: True and False. He worked out precise rules for expressions that are either entirely true or completely false. The word Boolean is capitalized out of deference to Charles Boole, a 19th-century mathematician and philosopher who wanted to apply mathematical principles to logic. Boolean Constants and Expressions in Python I promise we’ll come back and build the code, but it’ll be easier if we pack our toolkit first. However before writing the code for it, we need to take a fun side trip to the hardware store to pick up some other tools for the job. So now we know how to tell if a number is odd or even. We show that you can use other numbers with the modulo operator on line three. 5 % 2 does not divide evenly, so this does not return a zero. We see that the remainder of 4 modulo 2 is 0, which tells us it divides evenly or is an even number. We use the modulo operator, “%,” to calculate the remainder of a division: print(4 % 2) We know that a number that’s evenly divisible by two is even - that is to say, the remainder of the division will be zero. Perhaps we want to print a formatted string including “odd” if a number is odd and “even” if it’s even. Let’s take a simple example of determining whether a number is odd or even. You May Also Like A Simple Boolean Example in Python.Python If/Else and Booleans: Examples and Practice Questions.What Are the Precedence Rules For Python Boolean Expressions?.A Truth Table for Python Boolean Expressions.What Are Compound Boolean Expressions in Python?.Handling More Than Two Cases in Python: Elif.Boolean Constants and Expressions in Python.
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