11.5 Using modules with classes

Learning objectives

By the end of this section you should be able to

Construct an import statement that selectively imports classes.
Create an alias to import a module.

Importing classes from modules

Import statements, as discussed in the Modules chapter, allow code from other files, including classes, to be imported into a program. Accessing an imported class depends on whether the whole module is imported or only selected parts.

Multiple classes can be grouped in a module. For good organization, classes should be grouped in a module only if the grouping enables module reuse, as a key benefit of modules is reusability.

Using aliases

Aliasing allows the programmer to use an alternative name for imported items. Ex: import triangle as tri allows the program to refer to the triangle module as tri. Aliasing is useful to avoid name collisions but should be used carefully to avoid confusion.

Example 1 Using aliasing to import character

character.py

class Level:
  def __init__(self, level=1):
    self.level = level
    ...
  def level_up(self):
    ...
class XP:
  def __init__(self, XP=0):
    self.XP = XP
    ...
  def add_xp(self, num):
    ...

main.py


    import character as c
    
    bard_level = c.Level(1)
    bard_XP = c.XP(0)
    bard_XP.add_xp(300)
    bard_level.level_up()
    ...

Note

Missing import statement

Add the missing import statement to the top of the file. Do not make any changes to the rest of the code. In the end, the program should run without errors.

from math import sqrt
# Import statement

def is_prime(n):
    if n < 2:
        return False
    for i in range(2, int(sqrt(n)) + 1):
        if n % i == 0:
            return False
    return True

def test(num):
    for n in range(num):
        if is_prime(n):
            print(n, "is prime")
        else:
            print(n, "is NOT prime")

def pizza_rate(size, price):
    pizza = Circle(size/2)
    return price / pizza.area()

test(10)
print()
print("  Small for $4.99:", pizza_rate(10, 4.99))
print(" Medium for $5.99:", pizza_rate(12, 5.99))
print("  Large for $7.99:", pizza_rate(14, 7.99))
print("X-Large for $9.99:", pizza_rate(16, 9.99))

Note

Missing class import statement

Add the missing class import statement to the top of the file. Import only a class, not a full module. Do not make any changes to the rest of the code. In the end, the program should run without errors.

# Import statement

class Sequence:
    nums = [0, 1]

    def __init__(self):
        for i in range(2, 10):
            self.nums.append(self.nums[i-2] + self.nums[i-1])


fibs = Sequence()
print(fibs.nums)
sqs = Squares()
print(sqs.nums)

Adapted from Introduction to Python Programming by OpenStax (openstax.org), licensed under CC BY-NC-SA 4.0. Changes were made. License: CC-BY-NC-SA-4.0.