Python File Handling and File I/O

File handling in Python is a vital skill for working with external files to read, write, and manage data. Python provides a simple and intuitive interface for file operations through built-in functions and methods.

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Why File Handling is Important

File handling allows programs to: - Store data persistently. - Share data between programs. - Work with large datasets efficiently.

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Basic File Operations

Opening a File

The open() function is used to open a file. It returns a file object and supports the following modes:

Mode	Description
r	Read mode (default).
w	Write mode. Creates a file if it doesn't exist. Overwrites existing content.
x	Exclusive creation. Fails if the file exists.
a	Append mode. Creates the file if it doesn't exist.
b	Binary mode.
t	Text mode (default).
+	Open for both reading and writing.

Syntax

file = open("filename", "mode")

Example

# Open a file in read mode
data_file = open("data.txt", "r")
print(data_file.read())
data_file.close()

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Reading a File

Python provides multiple methods to read from a file.

• read(size): Reads the specified number of bytes. Reads the entire file if no size is provided.
• readline(): Reads a single line from the file.
• readlines(): Reads all lines and returns them as a list.

Example

# Reading a file
with open("data.txt", "r") as file:
    content = file.read()
    print(content)

# Reading line by line
with open("data.txt", "r") as file:
    for line in file:
        print(line.strip())

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Writing to a File

To write data to a file, use the write() or writelines() methods.

• write(string): Writes a string to the file.
• writelines(list): Writes a list of strings to the file.

Example

# Writing to a file
with open("output.txt", "w") as file:
    file.write("Hello, World!\n")
    file.write("Python File I/O is simple.")

# Writing multiple lines
lines = ["Line 1\n", "Line 2\n", "Line 3\n"]
with open("output.txt", "w") as file:
    file.writelines(lines)

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Appending to a File

Use the a mode to append data to a file without overwriting its existing content.

Example

# Appending data to a file
with open("output.txt", "a") as file:
    file.write("This is an appended line.\n")

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Closing a File

Always close a file after operations to free up system resources. This can be done explicitly using file.close() or automatically with a with statement.

Example

# Explicitly closing a file
file = open("data.txt", "r")
print(file.read())
file.close()

# Using a with statement
with open("data.txt", "r") as file:
    print(file.read())  # File is automatically closed after this block

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File Positioning

The seek() and tell() methods help navigate through a file.

• tell(): Returns the current file pointer position.
• seek(offset, from_what): Moves the file pointer to the specified position.
• from_what values: 0 (default, beginning of file), 1 (current position), 2 (end of file).

Example

with open("data.txt", "r") as file:
    print(file.read(5))      # Read first 5 bytes
    print(file.tell())       # Print current position
    file.seek(0)             # Move pointer to the beginning
    print(file.read(5))      # Read first 5 bytes again

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Working with Binary Files

Binary files store data in a non-human-readable format (e.g., images, videos).

Example

# Writing binary data
with open("image.png", "rb") as source:
    content = source.read()

with open("copy.png", "wb") as destination:
    destination.write(content)

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File Deletion

Use the os module to delete files.

Example

import os

# Deleting a file
if os.path.exists("output.txt"):
    os.remove("output.txt")
    print("File deleted.")
else:
    print("File does not exist.")

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Exception Handling in File Operations

Use try-except blocks to handle errors gracefully.

Example

try:
    with open("non_existent.txt", "r") as file:
        print(file.read())
except FileNotFoundError:
    print("File not found!")

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Summary of File I/O Methods

Method	Description
open()	Opens a file.
read()	Reads the entire file or specified bytes.
readline()	Reads a single line.
readlines()	Reads all lines as a list.
write()	Writes a string to the file.
writelines()	Writes a list of strings to the file.
close()	Closes the file.
seek()	Moves the file pointer to a specific position.
tell()	Returns the current file pointer position.

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File handling is a fundamental skill in Python, enabling programs to interact with external files effectively. Understanding these concepts will help you manage data efficiently in real-world applications.