Source: https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/3-2-1-data-flow [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) › Data Flow # Data Flow Coding: Introduction to Python v3, topic 3.2.1 ## Passing Parameters Passing parameters allows us to send data into a subroutine. ### Passing parameters ![Passing parameters](https://image-v2.cdn.app.senecalearning.com/2018-09/0013c8a8-e85c-4acd-a8de-79713db7ecab/post-403145_1280.png) - Passing parameters is the process of passing a piece of data into a subroutine. - The data is then assigned into a local variable (parameter) inside of the subroutine. - We can then use this data inside the subroutine. ### Parameters vs global variables ![Parameters vs global variables](https://image-v2.cdn.app.senecalearning.com/2018-08/eeeae8d9-efee-41bc-8e5e-23daff64465b/earth-1617121_1920.jpg) - We could also pass data by putting it inside of a global variable. - This is considered bad practice, since it can be accessed by any subroutine. Passing parameters is a much more secure, and maintainable approach. ## Returning Multiple Values Sometimes, a situation might arise where we wish to return multiple pieces of data from the same subroutine. ### Returning values ![Returning values](https://image-v2.cdn.app.senecalearning.com/2018-07/227b3f2c-0edd-4074-9406-bfa10b6e5ef2/Email-Internet-Message-Computer-.jpg) - Functions are subroutines that return a value. - In Python, a function can return multiple values. - These values are automatically grouped together (as a tuple). ### Returning a list ![Returning a list](https://image-v2.cdn.app.senecalearning.com/2018-09/3fba2487-0107-4ee7-9e33-50edfe5b6f04/checklist-ticklist-tick-list-.jpg) - Another solution is to return a list of values. - We can create a list and append each value we want to return. - This list can then be returned, containing all of the values. ### Restructuring subroutines ![Restructuring subroutines](https://image-v2.cdn.app.senecalearning.com/courseImages/chemistry/2.3.2%20Giant%20Covalent%20Structures/steel-girder.jpg) - In some scenarios, it may be better to restructure subroutines so they return a single value. - Returning multiple values is acceptable when the values are related. - If a function returns many unrelated values, it may be a sign that the function should be split into smaller functions. ## Test yourself on Data Flow - When data is passed as a parameter, it is assigned to what type of variable inside the subroutine? - Which is the best method to use in Python when multiple related values need to be returned from a function? [Practise this topic for free](https://app.senecalearning.com/classroom/course/72d0364c-db0a-4630-8e0a-61f48cae0252/section/422971de-7764-4b97-a32b-5c71176b88eb/session) - Previous topic: [3.1.1 Subroutines](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/3-1-1-subroutines.md) - Next topic: [4.1.1 Identifiers](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/4-1-1-identifiers.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)