7.2 Distinguish between built in functions and user defined functions

Distinguishing between Python built-in functions and user-defined functions can be done by understanding their characteristics and origins. Here's a detailed explanation of each:

7.2a Python Built-in Functions

1. Predefined - Built-in functions are pre-installed with Python and are available out-of-the-box.
2. Part of Python Standard Library - They are part of Python's standard library and are universally available in any Python environment.
3. Consistent Behavior - They have consistent behavior and are well-documented.
4. No Need for Definition - They do not require any user-defined code to be written; they can be used directly.

Examples:

• print() - Outputs text or other data to the console.
• len() - Returns the length of an object.
• sum() - Sums the items of an iterable.
• type() - Returns the type of an object.

Example 7.2.1 - with built-in functions.

# Using built-in functions
print("Hello, world!")  # Output: Hello, world!
length = len([1, 2, 3, 4])  # length is 4
total = sum([1, 2, 3, 4])  # total is 10
data_type = type(42)  # data_type is <class 'int'>

7.2b User-defined functions characteristics

1. Custom Definitions - User-defined functions are created by the programmer to perform specific tasks.
2. Defined Using def Keyword - They are defined using the def keyword followed by a function name and parentheses containing parameters.
3. Scope Limited to the Script/Module - They are available only within the script or module where they are defined unless explicitly imported elsewhere.
4. Flexible - They can be tailored to fit the specific needs of a program.

Examples of user-defined function are any function you define to perform a particular task. More examples are available in section 7.3 where we will learn how to create user-defined functions.

7.2c Summary of differences

7.2d Identifying Functions

To determine if a function is built-in or user-defined:

• Check Documentation - Built-in functions are documented in the Python Standard Library documentation.
• Source Code- User-defined functions are present in your script or module, and their definitions start with the def keyword.
• Use the builtins Module: You can inspect the builtins module to see all built-in functions available in Python.

By understanding these characteristics and using these methods, you can easily distinguish between built-in and user-defined functions in Python.