Chapter 7: Python – Functions & File
Handling
7.1 Functions in Python
A function is a reusable block of code that performs a specific task.
7.1.1 Types of Functions
1. Built-in Functions → Predefined functions (e.g., len(), print(), max()).
2. User-Defined Functions → Functions created by the programmer.
7.1.2 Defining a Function
Syntax:
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def function_name(parameters):
# function body
return value # (optional)
Example:
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def greet(name):
return "Hello, " + name
print(greet("Alice")) # Output: Hello, Alice
7.1.3 Calling a Function
A function is called using its name followed by parentheses:
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greet("Bob")
7.2 Function Parameters & Arguments
7.2.1 Types of Arguments
Type Description Example
Positional Arguments Values passed in order. greet("Alice")
Assigns a default value if not def
Default Arguments greet(name="Guest")
provided.
Type Description Example
Keyword Arguments Specifies parameters by name. greet(name="Charlie")
Variable-Length def sum(*numbers):
Allows multiple arguments.
Arguments
Example:
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def add(a, b=5): # Default argument
return a + b
print(add(3)) # Output: 8
print(add(3, 7)) # Output: 10
7.3 Types of Functions
7.3.1 Functions without Return Value
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def greet():
print("Hello, World!")
7.3.2 Functions with Return Value
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def square(num):
return num * num
print(square(4)) # Output: 16
7.3.3 Recursive Functions
A function that calls itself.
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def factorial(n):
if n == 0:
return 1
return n * factorial(n - 1)
print(factorial(5)) # Output: 120
7.4 Scope & Lifetime of Variables
7.4.1 Local & Global Variables
Variable Type Scope Example
Local Variable Exists inside a function only. def func(): x = 10
Global Variable Available throughout the program. x = 100
Example:
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x = 50 # Global Variable
def func():
x = 10 # Local Variable
print(x) # Output: 10
func()
print(x) # Output: 50
7.5 File Handling in Python
7.5.1 Introduction to File Handling
Python can read and write files using file handling operations.
7.5.2 File Operations
Mode Symbol Description
Read r Opens file for reading (default mode).
Write w Opens file for writing (erases existing content).
Append a Opens file for appending (adds to the end).
Read & Write r+ Reads and writes to a file.
Binary rb, wb, ab Reads/writes in binary mode.
Example (Opening a file in read mode):
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file = open("example.txt", "r")
content = file.read()
print(content)
file.close()
7.6 Reading & Writing Files
7.6.1 Writing to a File
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file = open("example.txt", "w")
file.write("Hello, Python!")
file.close()
If the file doesn’t exist, it will be created.
If the file exists, old content is deleted.
7.6.2 Reading from a File
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file = open("example.txt", "r")
print(file.read()) # Reads entire file content
file.close()
7.6.3 Appending to a File
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file = open("example.txt", "a")
file.write("\nNew line added.")
file.close()
Appends data instead of overwriting existing content.
7.7 Working with File Methods
Method Description
read() Reads the entire file.
readline() Reads a single line from the file.
readlines() Reads all lines into a list.
write() Writes data to the file.
writelines() Writes multiple lines from a list.
Example (readlines() method):
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file = open("example.txt", "r")
lines = file.readlines()
for line in lines:
print(line.strip()) # Removes extra newline
file.close()
7.8 Using with Statement for File Handling
The with statement automatically closes the file after use.
Example:
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with open("example.txt", "r") as file:
content = file.read()
print(content)
# No need for file.close()
7.9 Handling Exceptions in File Operations
If a file does not exist, attempting to read it will cause an error.
7.9.1 Handling Errors Using try-except
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try:
file = open("nonexistent.txt", "r")
print(file.read())
except FileNotFoundError:
print("File not found!")
Prevents the program from crashing if the file is missing.
Summary of Chapter 7
Functions → Reusable blocks of code.
Types of Functions → Built-in, User-defined, Recursive.
Arguments → Positional, Default, Keyword, Variable-length.
Scope → Local and Global variables.
File Handling → Read, Write, Append modes.
File Methods → read(), write(), readlines().
Exception Handling → Prevents file-related errors.
