Constants

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Which line follows the Python convention for naming a constant?

A GST_RATE = 0.1

B gstRate = 0.1

2. Where should constants normally be defined in a program?

A At the top of the program, before they are used

B Buried in the middle of a loop

3. Which statement about a constant is correct?

A Its value is set once and not changed while the program runs

B Its value changes every time the user enters data

4. Which one is best stored as a constant?

A score = 0

B MAX_ATTEMPTS = 3

5. Which line avoids a 'magic number'?

A total = price * 0.1

B total = price * GST_RATE

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1GST_RATE = 0.1		ADefines a constant named GST_RATE with the value 0.1, set once and not changed while the program runs
2total = price * GST_RATE		BThe constant is written in lower case. By convention constants use UPPER_CASE, such as GST_RATE, so readers know it must not change.
3A magic number is an unexplained value typed directly into code, which a named constant avoids		CThe constant is reassigned partway through the program. A constant must be set once and never changed while the program runs.
4A variable can change as the program runs, but a constant should stay the same		DUses the constant's name instead of a magic number, so the 0.1 is not hard-coded in the calculation
5gst_rate = 0.1		Escore = score + 1
6GST_RATE = 0.1 GST_RATE = 0.15		Ftax = price * 0.1

Definitions

GST_RATE = 0.1

Fill in the Blanks

Complete each line of code by filling in the missing parts.

________ = 0.1

GST _ 0.1

total = price * (1 + ________)

if score >= _________:

seconds = minutes _ SECONDS_PER_MINUTE

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A GST_RATE = 0.1

B price = 50

C gst = price * GST_RATE

D total = price + GST_RATE

E print(total)

Question 2

A MAX_ITEMS = 5

B items = 0

C items = items + 1

D if items > max_items:

E print("Full")

Question 3

A PI = 3.14159

B radius = 4

C area = 3.14159 * radius ** 2

D print(area)

Question 4

A TAX_RATE = 0.1

B price = "200"

C tax = price * TAX_RATE

D print(tax)

Question 5

A MAX SPEED = 100

B speed = 80

C if speed > MAX_SPEED:

D print("Too fast")

Answer Key

Constants

Section A: Quick Questions

A — GST_RATE = 0.1

A — At the top of the program, before they are used

A — Its value is set once and not changed while the program runs

B — MAX_ATTEMPTS = 3

B — total = price * GST_RATE

Section B: Match the Pairs

GST_RATE = 0.1 → Defines a constant named GST_RATE with the value 0.1, set once and not changed while the program runs

total = price * GST_RATE → Uses the constant's name instead of a magic number, so the 0.1 is not hard-coded in the calculation

A magic number is an unexplained value typed directly into code, which a named constant avoids → tax = price * 0.1

A variable can change as the program runs, but a constant should stay the same → score = score + 1

gst_rate = 0.1 → The constant is written in lower case. By convention constants use UPPER_CASE, such as GST_RATE, so readers know it must not change.

GST_RATE = 0.1 GST_RATE = 0.15 → The constant is reassigned partway through the program. A constant must be set once and never changed while the program runs.

Section C: Definitions

GST_RATE = 0.1 — A constant: a named value set once and never changed while the program runs. Written in UPPER_CASE by convention, it replaces magic numbers and is easy to update in one place.

Section D: Fill in the Blanks

GST_RATE = 0.1

GST = 0.1

total = price * (1 + GST_RATE)

if score >= PASS_MARK:

seconds = minutes * SECONDS_PER_MINUTE

Section E: Spot the Error

D — This adds the rate (0.1) to the price instead of the GST amount. It should be total = price + gst.

D — The constant was defined as MAX_ITEMS in upper case. Python is case-sensitive, so max_items causes a NameError. It should be MAX_ITEMS.

C — This types the number directly (a magic number) instead of using the constant PI. It should be area = PI * radius ** 2.

B — The quotes make price a string, so multiplying it by the float TAX_RATE causes a TypeError. It should be price = 200.

A — Names cannot contain spaces, so this is a syntax error. Use an underscore: MAX_SPEED = 100.