Source: https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/3-1-1-subroutines [Revision notes](https://senecalearning.com/en-gb/revision-notes.md) › [GCSE](https://senecalearning.com/en-gb/revision-notes/gcse.md) › [Coding](https://senecalearning.com/en-gb/revision-notes/gcse/coding.md) › [National Curriculum](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum.md) › Subroutines # 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](https://image-v2.cdn.app.senecalearning.com/2018-07/95d17dd9-261f-4238-9065-f411ea8c7210/code-Data-Computer-Wifi-Internet.jpg) - 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](https://image-v2.cdn.app.senecalearning.com/2018-07/c45f4db9-a761-4a23-9c16-be48190066bc/2.2.4%20Parameters%20vs%20arguments.png) - 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](https://image-v2.cdn.app.senecalearning.com/2018-07/44bd33c3-2cd5-453e-9359-41ccb52ffc84/2.2.4%20Types%20of%20subroutine.png) - 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](https://image-v2.cdn.app.senecalearning.com/2018-07/8b8802c8-d4ac-4692-a407-e4ca1a5aa044/IP-Address-Code-Computer-Monitor-Screen-.jpg) - 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](https://image-v2.cdn.app.senecalearning.com/2018-07/423dbff4-848f-43f6-934b-ce8dde8c95c9/Internet-World-Computer-Networks-Wireless-.jpg) - 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](https://image-v2.cdn.app.senecalearning.com/courseImages/physics/1.5.2%20-%20Energy%20resources/recycle-29227_640-min.jpg) - 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](https://image-v2.cdn.app.senecalearning.com/2018-09/11f1567f-060b-4155-952f-3cc14b8b3a66/large-pile.jpg) - 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? [Practise this topic for free](https://app.senecalearning.com/classroom/course/72d0364c-db0a-4630-8e0a-61f48cae0252/section/acfc2d66-1bf9-4980-907d-ee9747ccc021/session) - Previous topic: [2.2.1 File Handling](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/2-2-1-file-handling.md) - Next topic: [3.2.1 Data Flow](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/3-2-1-data-flow.md) ## Coding: Introduction to Python v3 contents ### 1 Introduction to Python - 1.1 Python - [1.1.1 Python](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/1-1-1-python.md) - 1.2 Input & Output - [1.2.1 Input & Output](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/1-2-1-input-and-output.md) - 1.3 Data Types - [1.3.1 Data Types](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/1-3-1-data-types.md) - 1.4 Variables & Constants - [1.4.1 Variables & Constants](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/1-4-1-variables-and-constants.md) - 1.5 Operators - [1.5.1 Arithmetic & Relational Operators](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/1-5-1-arithmetic-and-relational-operators.md) - [1.5.2 Boolean & Assignment Operators 2](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/1-5-2-boolean-and-assignment-operators-2.md) - 1.6 Program Flow - [1.6.1 Selection](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/1-6-1-selection.md) - [1.6.2 Iteration](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/1-6-2-iteration.md) ### 2 Data Structures - 2.1 Lists & Strings - [2.1.1 Lists](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/2-1-1-lists.md) - [2.1.2 Strings](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/2-1-2-strings.md) - 2.2 File Handling - [2.2.1 File Handling](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/2-2-1-file-handling.md) ### 3 Modularity - 3.1 Subroutines - [3.1.1 Subroutines](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/3-1-1-subroutines.md) - 3.2 Data Flow - [3.2.1 Data Flow](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/3-2-1-data-flow.md) ### 4 Good Practice - 4.1 Naming & Whitespace - [4.1.1 Identifiers](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/4-1-1-identifiers.md) - [4.1.2 Whitespace](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/4-1-2-whitespace.md) - 4.2 Comments - [4.2.1 Comments](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/4-2-1-comments.md) - 4.3 Exceptions - [4.3.1 Exceptions](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/4-3-1-exceptions.md)