REFERENCEpython

python Documentation

📖 INDEX

# print

# arithmetic-operators

# assignment-operators

# comparison-operators

# logical-operators

# identity-operators

# membership-operators

# keyword-arguments-kwargs

# default-parameter-value

# class-methods-classmethod

# static-methods-staticmethod

# dunder-methods

# try-block

# except-block

# else-block-exceptions

# list-comprehensions

# dictionary-comprehensions

# set-comprehensions

# iterators

# property-decorator-property

# context-managers-contextmanager

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def Keyword

AI & DATA SCIENCE // def-keyword

def defines a function — a named, reusable block of code that can accept parameters and optionally return a value.

Syntax

def function_name(param1, param2):
    # function body
    return result

Deep Dive Course

def creates a function object and binds it to a name in the current scope — functions are first-class objects in Python, meaning they can be assigned to variables, passed as arguments, stored in data structures, and returned from other functions, just like any other value. The body is defined by indentation, and an optional docstring as the first statement documents what the function does for tools like help().

1Understanding def Keyword

💡

Write a one-line docstring under the def line for any function whose purpose isn't immediately obvious from its name and parameters — it costs almost nothing and pays off the next time you or a teammate needs help().

editor.html

def greet(name):
    """Return a friendly greeting for name."""
    return f"Hello, {name}!"

print(greet("Alice"))

localhost:3000

2Practical Example

Here is a real-world application of def Keyword showing how it is used in production Python code.

editor.html

def apply_twice(func, value):
    return func(func(value))

print(apply_twice(lambda x: x * 2, 3))

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3Best Practices

Follow these guidelines when working with def Keyword:

1. Give functions clear, verb-based names that describe what they do

2. Write a docstring for any non-trivial function so help() and IDE tooltips are actually useful

3. Keep functions focused on one responsibility — if a function needs 'and' to describe what it does, consider splitting it

⚠️

Tip: Write a one-line docstring under the def line for any function whose purpose isn't immediately obvious from its name and parameters — it costs almost nothing and pays off the next time you or a teammate needs help().

editor.html

def greet(name):
    """Return a friendly greeting for name."""
    return f"Hello, {name}!"

print(greet("Alice"))

localhost:3000

Examples

Example 01Basic Usage

def greet(name):
    """Return a friendly greeting for name."""
    return f"Hello, {name}!"

print(greet("Alice"))

Example 02Advanced Example

def apply_twice(func, value):
    return func(func(value))

print(apply_twice(lambda x: x * 2, 3))

Best Practices

Give functions clear, verb-based names that describe what they do
Write a docstring for any non-trivial function so help() and IDE tooltips are actually useful
Keep functions focused on one responsibility — if a function needs 'and' to describe what it does, consider splitting it

Interview Question

In what sense are Python functions 'first-class objects', and why does that matter?▼

Hint: Think about what you can do with a function besides calling it.

Being first-class means a function is a regular value, just like a number or a string: it can be assigned to a variable, stored in a list or dict, passed as an argument to another function, and returned as a result. This is what makes patterns like passing a callback, building a dispatch table of functions, or writing decorators possible in Python without any special syntax beyond what the language already provides for other values.

Exercises

MediumPractice using def Keyword in a real scenario.

View Solution

def greet(name):
    """Return a friendly greeting for name."""
    return f"Hello, {name}!"

print(greet("Alice"))

Frequently Asked Questions

In what sense are Python functions 'first-class objects', and why does that matter?▼

Related Functions

return-statementlambda-functionsdecorators