Names are given to values in Python using an assignment statement. In an assignment, a name is followed by
=, which is followed by any expression. The value of the expression to the right of
= is assigned to the name. Once a name has a value assigned to it, the value will be substituted for that name in future expressions.
a = 10 b = 20 a + b
A previously assigned name can be used in the expression to the right of
quarter = 1/4 half = 2 * quarter half
However, only the current value of an expression is assigned to a name. If that value changes later, names that were defined in terms of that value will not change automatically.
quarter = 4 half
Names must start with a letter, but can contain both letters and numbers. A name cannot contain a space; instead, it is common to use an underscore character
_ to replace each space. Names are only as useful as you make them; it’s up to the programmer to choose names that are easy to interpret. Typically, more meaningful names can be invented than
b. For example, to describe the sales tax on a $5 purchase in Berkeley, CA, the following names clarify the meaning of the various quantities involved.
purchase_price = 5 state_tax_rate = 0.075 county_tax_rate = 0.02 city_tax_rate = 0 sales_tax_rate = state_tax_rate + county_tax_rate + city_tax_rate sales_tax = purchase_price * sales_tax_rate sales_tax