Master Python Functions: From Basics to Advanced Module Usage

Quick Introduction to Functions

A function is an independent block of code packaged as a small module that can be invoked when needed, improving development efficiency and code reuse.

Basic Usage

Defining a function follows the format:

<code>def function_name():
    # function body
    ...
</code>

Key points:

def is short for define .

The function name should clearly express its purpose and follow identifier rules (letters, underscores, digits; cannot start with a digit or clash with keywords).

Calling a function is as simple as writing function_name() .

First Function Example

<code>name = "小明"

def say_hello():
    print("hello 1")
    print("hello 2")
    print("hello 3")

print(name)
say_hello()
print(name)
</code>

Note that a function does nothing until it is explicitly called; otherwise a NameError will be raised.

Parameters

Parameters make functions reusable for different data. Define them inside the parentheses and separate multiple parameters with commas.

<code>def sum_2_num(num1, num2):
    result = num1 + num2
    print("%d + %d = %d" % (num1, num2, result))

sum_2_num(50, 20)
</code>

Formal parameters (the ones in the definition) receive the values passed as actual arguments during the call.

Return Values

Use return to send a result back to the caller. The caller can capture it with a variable.

<code>def sum_2_num(num1, num2):
    """Add two numbers"""
    return num1 + num2

result = sum_2_num(10, 20)
print("计算结果是 %d" % result)
</code>

After a return statement, no further code in the function is executed.

Nested Calls

A function can call another function, creating nested execution.

<code>def test1():
    print("*" * 50)
    print("test 1")
    print("*" * 50)

def test2():
    print("-" * 50)
    print("test 2")
    test1()
    print("-" * 50)

test2()
</code>

Practical Exercises

Various print_line functions demonstrate parameter usage and code reuse:

<code>def print_line(char):
    print("*" * 50)

def print_line(char):
    print(char * 50)

def print_line(char, times):
    print(char * times)

def print_lines(char, times):
    row = 0
    while row < 5:
        print_line(char, times)
        row += 1
</code>

Using Functions from Modules

Modules are Python files ( .py ) that can contain variables and functions. Import them with import and access their contents via module_name.attribute .

<code>name = "程序员"
import hm_10_分隔线模块
hm_10_分隔线模块.print_line("-", 80)
print(hm_10_分隔线模块.name)
</code>

When a module is imported, Python may generate a compiled byte‑code file ( .pyc ) in a __pycache__ directory. This speeds up subsequent runs by skipping the compilation step if the source has not changed.

Debugging with PyCharm

F8 (Step Over) executes a line, treating a function call as a single step.

F7 (Step Into) dives into the function body to debug line by line.

Documentation Strings

Place a triple‑quoted string immediately after the function definition to describe its purpose. Press Ctrl+Q in PyCharm to view the docstring while calling the function.

Note: Keep two blank lines before a function definition to separate it from other code or comments.