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F4.5 Libraries and your own modules

Functions and structured code · GCSE · OCR J277 2.2.3, AQA 8525 3.2.10, Edexcel 1CP2 6.6.1 · about 15 min

What this lesson is about

import, Python's own libraries, and a module file of your own.

• import
• Three ways to import
• Libraries you already know
• Your own module
• Why write modules?

Questions 5 marks in all

1. [1 mark]What does this program print?

   import math
   print(math.sqrt(49))

   Answer:

   7.0

   sqrt from the math library gives a real number, so 7.0.

2. [1 mark]What does this program print?

   from math import floor, ceil
   print(floor(2.7), ceil(2.1))

   Answer:

   2 3

   from ... import brings in just those names; floor rounds down and ceil rounds up.

3. [1 mark]Which are benefits of using a library?

   Tick every answer that is true.

   1. AIt saves writing the code yourself
   2. BIts code has already been tested
   3. CYou can use complex features without knowing how they work
   4. DIt makes every program shorter than 10 lines
   Answer: A, B, C. Libraries save time and effort and are usually well tested.

4. [1 mark]A program says import moves and calls moves.square(20). Where is square defined?

   1. AIn a file called moves.py
   2. BInside the program itself
   3. CIn the math library
   4. DNowhere: it causes an error
   Answer: A. import moves loads the module moves.py, and moves.square reaches the function in it.

5. [1 mark]Why does moves.py need its own from bugbot import * line?

   1. AA module gets the robot's commands only by importing them itself
   2. BEvery Python file must start with it
   3. CIt connects to the robot twice
   4. DIt does not need it
   Answer: A. Each file has its own names, so a module that uses forward must import it.

The task: use your module

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

import moves

moves.square(20)

{'program': 'from bugbot import *\nconnect()\nimport moves\n\nmoves.square(20)\nmoves.square(35)\n', 'files': {'moves.py': '# moves.py: driving moves, for any program that imports it\nfrom bugbot import *\n\ndef zigzag(length):\n    """Drive a zigzag: forward and right, then forward and left."""\n    forward(60, distance=length)\n    right(60, distance=length)\n    forward(60, distance=length)\n    left(60, distance=length)\n\ndef square(size):\n    """Drive a square with sides of size cm, ending where it started."""\n    forward(60, distance=size)\n    right(60, distance=size)\n    backward(60, distance=size)\n    left(60, distance=size)\n'}}