Source: https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/4-1-1-identifiers

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# Identifiers

Coding: Introduction to Python v3, topic 4.1.1

## Identifiers

Identifiers are the names given to variables, constants, and subroutines.

### Variables

![Variables](https://image-v2.cdn.app.senecalearning.com/2018-07/050c73a9-e0c2-4651-b3f6-54dd46acdf0d/RAM-Random-Access-Memory-Computer-.jpg)

- In Python, variables should have lowercase names, with each word separated by an underscore. For example:
 - this_is_my_variable
 - user_money 
- Variable should also have descriptive names, for example user_money is much better than this_is_my_variable.

### Constants

![Constants](https://image-v2.cdn.app.senecalearning.com/2018-05/d02fc304-19d2-4611-a75e-08d788b5e2cd/letters-656514_960_720.png)

- Constants should be named using the same rules as variables, but uppercase.

### Subroutines

![Subroutines](https://image-v2.cdn.app.senecalearning.com/2018-09/e3db2cf8-61a4-43d4-804a-45efd9569613/flow-diagram.jpg)

- Subroutines should have lowercase names, with each word separated by an underscore. For example:
 - calculate_sum()
 - get_user_id()
- Subroutines should have descriptive names where possible.

### Global rules

![Global rules](https://image-v2.cdn.app.senecalearning.com/2018-09/d4d7be69-e7c0-4540-94bf-fd7f5e635625/moon-earth-space-.jpg)

- In general, all identifiers should be descriptive.
- Characters which might be confused should be avoided, for example:
 - 0 and O.
 - 1 and l (lower case L).

## Test yourself on Identifiers

- Which character should separate each word in variable and constant identifiers?
- Which of the following are suitable names for constants?

[Practise this topic for free](https://app.senecalearning.com/classroom/course/72d0364c-db0a-4630-8e0a-61f48cae0252/section/010da0dc-2f59-4d44-bcdc-c2390049d82b/session)

- Previous topic: [3.2.1 Data Flow](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/3-2-1-data-flow.md)
- Next topic: [4.1.2 Whitespace](https://senecalearning.com/en-gb/revision-notes/gcse/coding/national-curriculum/4-1-2-whitespace.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)