Python: Expressions

Expressions

• Expression is a combination of values, variables and operators.

• Value is considered as an expression.

• For example: Following are expressions

a=10

a+20

30

2+3*4

14

The first statement in above code is the assignment statement. The second statement is an expression. The interpreter evaluates the expression and displays the result.

Order of execution

• When more than one operator appears in an expression, the order of evaluation depends on the rules of precedence.

• Python follows the same precedence rules for its mathematical operators that mathematics does.

The acronym PEMDAS is a useful way to remember the order of operations.

1.  P: Parentheses have the highest precedence and can be used to force an expression to evaluate in the order you want. Since expressions in parentheses are evaluated first, 1 * (10‒5) is 5.

2.  E: Exponentiation has the next highest precedence, so 2**3 is 8.

3.  MDAS: Multiplication and Division have the same precedence, which is higher than Addition and Subtraction, which also have the same precedence. So 2+3*4 yields 14 rather than 20.

4. Operators with the same precedence are evaluated from left to right. So in the expression 3‒2+1 will result 2. As subtraction is performed first and then addition will be performed.

Review Questions

1. What is a numeric literal? Give an example.

2. Outline the operator precedence of arithmetic operators in Python.

3. Mention the list of keywords available in python. Compare it with variable names.

4.What are the statements? How are they constructed from variable and expressions in python?

5. What are keywords? Give examples.