Subroutines

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Subroutines

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

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

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

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

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

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

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.

1Introduction to Python

1.1Python

1.1.1Python

1.2Input & Output

1.2.1Input & Output

1.3Data Types

1.3.1Data Types

1.4Variables & Constants

1.4.1Variables & Constants

1.5Operators

1.5.1Arithmetic & Relational Operators

1.5.2Boolean & Assignment Operators 2

1.6Program Flow

1.6.1Selection

1.6.2Iteration

2Data Structures

2.1Lists & Strings

2.1.1Lists

2.1.2Strings

2.2File Handling

2.2.1File Handling

3Modularity

3.1Subroutines

3.1.1Subroutines

3.2Data Flow

3.2.1Data Flow

4Good Practice

4.1Naming & Whitespace

4.1.1Identifiers

4.1.2Whitespace

4.2Comments

4.2.1Comments

4.3Exceptions

4.3.1Exceptions

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