PrintYou are already familiar with Python binary operators that can be used to define arbitrarily complex expressions. For instance, you can use arithmetic expressions that evaluate to a number, or boolean expressions that evaluate to either True or False. Here is an example of an arithmetic expression using the arithmetic operators – and *:
x = 25 – 2 * 3
Each binary operator takes two operand values of a particular type (all numbers in this example) and replaces them by a new value calculated from the operands. All Python operators are organized into different precedence classes, determining in which order the operators are applied when the expression is evaluated unless parentheses are used to explicitly change the order of evaluation. This operator precedence table shows the classes from lowest to highest precedence. The operator * for multiplication has a higher precedence than the – operator for subtraction, so the multiplication will be performed first and the result of the overall expression assigned to variable x is 19.
Here is an example for a boolean expression:
x = y > 12 and z == 3
The boolean expression on the right side of the assignment operator contains three binary operators: two comparison operators, > and ==, that take two numbers and return a boolean value, and the logical ‘and’ operator that takes two boolean values and returns a new boolean (True only if both input values are True, False otherwise). The precedence of ‘and’ is lower than that of the two comparison operators, so the ‘and’ will be evaluated last. So if y has the value 6 and z the value 3, the value assigned to variable x by this expression will be False because the comparison on the left side of the ‘and’ evaluates to False.
In addition to all these binary operators, Python has a ternary operator, so an operator that takes three operands as input. This operator has the format
x if c else y
x, y, and c here are the three operands while ‘if’ and ‘else’ are the keywords making up the operator and demarcating the operands. While x and y can be values or expressions of arbitrary type, the condition c needs to be a boolean value or expression. What the operator does is it looks at the condition c and if c is True it evaluates to x, else it evaluates to y. So for example in the following line of code
p = 1 if x > 12 else 0
variable p will be assigned the value 1 if x is larger than 12, else p will be assigned the value 0. Obviously what the ternary if-else operator does is very similar to what we can do with an if or if-else statement. For instance, we could have written the previous code as
p = 1
if x > 12:
p = 0
The “x if c else y” operator is an example of a language construct that does not add anything principally new to the language but enables writing things more compactly or more elegantly. That’s why such constructs are often called syntactic sugar. The nice thing about “x if c else y” is that in contrast to the if-else statement, it is an operator that evaluates to a value and, hence, can be embedded directly within more complex expressions as in the following example that uses the operator twice:
newValue = 25 + (10 if oldValue < 20 else 44) / 100 + (5 if useOffset else 0)
Using an if-else statement for this expression would have required at least five lines of code.