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Subroutines

Coding: Introduction to Python v3, topic 3.1.1

Subroutines

A subroutine is a named block of code within your program.

Advantages of subroutines

Advantages of subroutines

  • Easier to read:
  • There are fewer long blocks of code to understand.
  • More efficient:
  • Blocks of code can be written once and reused many times.
  • More reliable:
  • Each subroutine can be individually tested to ensure it works.
Parameters and arguments

Parameters and arguments

  • Parameters are special variables used to pass values into a subroutine.
  • Arguments are the actual values that are passed in.
Types of subroutine

Types of subroutine

  • A function is a subroutine which returns a value.
  • A procedure is a subroutine which does not return a value.

Scope

The scope of a variable is the group of areas of the code from which it can be accessed.

Local scope

Local scope

  • A variable defined within a subroutine will have local scope.
  • This means that they can only be accessed within that subroutine.
Global scope

Global scope

  • A variable can be made global by adding the 'global' keyword in front of it when it is first used.
  • Global variables may be accessed by any part of the whole program.

What Should be in a Subroutine?

Subroutines are key to maintainable code, but must be used correctly.

Good ideas for subroutines

Good ideas for subroutines

  • Subroutines should include single processes only.
  • Subroutines should ideally be designed so that they can be reused in multiple parts of code, both within and outside of your program.
  • Good examples of subroutines include:
  • Calculating the sum of a list.
  • Finding a largest element of a list.
  • Opening a specific part of an application.
Bad ideas for subroutines

Bad ideas for subroutines

  • Subroutines should not be used for very long processes
  • Subroutines should be split into multiple subroutines so that they don’t often exceed about 30 lines of code.
  • Bad examples of subroutines include:
  • The whole application.
  • A very specific, and non-reusable piece of code.

Test yourself on Subroutines

  • In the following code, is x a parameter or an argument?

    def name(x, y):  
    return x + y  

  • What is an argument of a subroutine?

  • What is global scope?

  • Which of the following are good examples of subroutines?

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