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Introduction to Python Programming

11.5 Using modules with classes

Introduction to Python Programming11.5 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.

Checkpoint

Importing classes from files

Concepts in Practice

Importing classes

1.
Consider the example above. How many classes are imported in the second main.py?
  1. 1
  2. 2
  3. 3
2.
Which line imports only the Level class from character?
  1. import Level from character
  2. from character import Level
  3. import Level
3.
How many classes can be in a module?
  1. none
  2. only 1
  3. any number

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 11.3

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()
    ...
    

Concepts in Practice

Using an alias

Consider the example above. Suppose a program imports the character module using import character as game_char.

4.
How would the program create a Level instance?
  1. rogue_level = character.Level()
  2. rogue_level = game_char.Level()
  3. rogue_level = character.game_char.Level()
5.
Which code creates a name collision?
  1. character = 'Ranger'
  2. Game_char = 'Ranger'
  3. game_char = 'Ranger'

Try It

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.

Try It

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.

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