Practical Programming, 2nd Edition

Variables and Computer Memory: Remembering Values

Like mathematicians, programmers frequently name values so that they can use them later. A name that refers to a value is called a variable. In Python, variable names can use letters, digits, and the underscore symbol (but they can’t start with a digit). For example, X, species5618, and degrees_celsius are all allowed, but 777 isn’t (it would be confused with a number), and neither is no-way! (it contains punctuation).

You create a new variable by assigning it a value:

>>> degrees_celsius = 26.0

This statement is called an assignment statement; we say that degrees_celsius is assigned the value 26.0. That makes degrees_celsius refer to the value 26.0. We can use variables anywhere ...