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18 Chapter 2. Variables, expressions and statements

keyword: A reserved word that is used by the compiler to parse a program; you cannot
use keywords like if, def, and while as variable names.
operator: A special symbol that represents a simple computation like addition, multipli-
cation, or string concatenation.

operand: One of the values on which an operator operates.
floor division: The operation that divides two numbers and chops off the fraction part.

expression: A combination of variables, operators, and values that represents a single re-
sult value.

evaluate: To simplify an expression by performing the operations in order to yield a single
value.

rules of precedence: The set of rules governing the order in which expressions involving
multiple operators and operands are evaluated.

concatenate: To join two operands end-to-end.
comment: Information in a program that is meant for other programmers (or anyone read-
ing the source code) and has no effect on the execution of the program.

2.12 Exercises

Exercise 2.3. Assume that we execute the following assignment statements:

width = 17
height = 12.0
delimiter = '.'
For each of the following expressions, write the value of the expression and the type (of the value of
the expression).

1. width/2
2. width/2.0
3. height/3

4. 1 + 2 * 5
5. delimiter * 5

Use the Python interpreter to check your answers.
Exercise 2.4. Practice using the Python interpreter as a calculator:

4
3
1. The volume of a sphere with radius r is πr . What is the volume of a sphere with radius 5?
3
Hint: 392.7 is wrong!
2. Suppose the cover price of a book is $24.95, but bookstores get a 40% discount. Shipping costs
$3 for the first copy and 75 cents for each additional copy. What is the total wholesale cost for
60 copies?
3. If I leave my house at 6:52 am and run 1 mile at an easy pace (8:15 per mile), then 3 miles at
tempo (7:12 per mile) and 1 mile at easy pace again, what time do I get home for breakfast?