Functions and Modules in Python: A Comprehensive Guide
1. Defining and Calling Functions
Defining Functions
A function in Python is a block of reusable code designed to perform a specific task. Functions are defined using the def keyword followed by the function name and parentheses ().
Syntax:
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def function_name(parameters):
“””
Docstring: Optional description of the function.
“””
# Function body
statement(s)
Example:
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def greet(name):
“””
This function greets the person passed in as a parameter.
“””
print(f”Hello, {name}!”)
greet(“Naeem”)
Calling Functions
Once a function is defined, it can be called by using its name followed by parentheses ().
Example:
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greet(“Naeem”) # Output: Hello, Naeem!
2. Function Arguments and Return Values
Function Arguments
Arguments are the values passed into a function. They can be of various types, such as positional arguments, keyword arguments, default arguments, and variable-length arguments.
Positional Arguments: Arguments that need to be included in the correct order.
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def add(a, b):
return a + b
result = add(5, 3) # 8
Keyword Arguments: Arguments that are passed by explicitly stating the parameter name.
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def greet(name, message):
print(f”{message}, {name}!”)
greet(name=”Naeem”, message=”Good Morning”) # Good Morning, Naeem!
Default Arguments: Arguments that assume a default value if no value is provided.
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def greet(name, message=”Hello”):
print(f”{message}, {name}!”)
greet(“Naeem”) # Hello, Naeem!
greet(“Naeem”, “Good Morning”) # Good Morning, Naeem!
Variable-Length Arguments: Functions can accept a variable number of arguments using *args (for non-keyword arguments) and **kwargs (for keyword arguments).
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def sum_all(*args):
return sum(args)
print(sum_all(1, 2, 3, 4)) # 10
def print_info(**kwargs):
for key, value in kwargs.items():
print(f”{key}: {value}”)
print_info(name=”Naeem”, age=25)
# name: Naeem
# age: 25
Return Values
Functions can return values using the return statement. If no return statement is used, the function will return None by default.
Example:
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def square(x):
return x * x
result = square(4) # 16
3. Lambda Functions
Lambda functions are small anonymous functions defined using the lambda keyword. They can take any number of arguments but have only one expression.
Syntax:
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lambda arguments: expression
Example:
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square = lambda x: x * x
print(square(5)) # 25
add = lambda a, b: a + b
print(add(3, 4)) # 7
Lambda functions are often used for short, throwaway functions or when a function is required as an argument to higher-order functions like map(), filter(), and reduce().
Example with map():
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numbers = [1, 2, 3, 4]
squared_numbers = list(map(lambda x: x * x, numbers))
print(squared_numbers) # [1, 4, 9, 16]
4. Modules and Packages
Modules
A module is a file containing Python code. It can define functions, classes, and variables, and can also include runnable code. Modules help organize code and reuse it across multiple programs.
Creating a Module: Create a file named mymodule.py:
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# mymodule.py
def greet(name):
print(f”Hello, {name}!”)
Using a Module:
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import mymodule
mymodule.greet(“Naeem”) # Hello, Naeem!
Packages
A package is a way of organizing related modules into a directory hierarchy. A package contains a special __init__.py file, which can be empty or contain package initialization code.
Creating a Package:
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mypackage/
__init__.py
module1.py
module2.py
Using a Package:
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# mypackage/module1.py
def function1():
print(“Function 1 from module 1”)
# mypackage/module2.py
def function2():
print(“Function 2 from module 2”)
# main.py
from mypackage import module1, module2
module1.function1() # Function 1 from module 1
module2.function2() # Function 2 from module 2
5. Importing and Using Modules
Importing Modules
Modules can be imported using the import statement. You can import an entire module, specific attributes, or use an alias for the module.
Importing an Entire Module:
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import math
print(math.sqrt(16)) # 4.0
Importing Specific Attributes:
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from math import sqrt, pi
print(sqrt(16)) # 4.0
print(pi) # 3.141592653589793
Using Aliases:
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import math as m
print(m.sqrt(16)) # 4.0
Importing from Packages
When importing from a package, you can use the from keyword to import specific modules or functions.
Example:
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from mypackage.module1 import function1
function1() # Function 1 from module 1
Built-in and Third-Party Modules
Python includes many built-in modules, and additional modules can be installed using package managers like pip.
Built-in Modules:
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import os
print(os.getcwd()) # Current working directory
Third-Party Modules:
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# Install a third-party module using pip:
# pip install requests
import requests
response = requests.get(“https://api.github.com")
print(response.status_code) # 200
Conclusion
Understanding functions and modules is fundamental to writing efficient and organized Python code. Functions enable code reuse and modularity, while modules and packages help in organizing and managing code in larger projects. By leveraging these features, you can create robust and maintainable Python applications.
