File handling

File Handling in Python

File handling in Python allows you to read from and write to files on your computer. Python provides built-in functions for working with files, and the most common methods for file handling are provided by the open(), read(), write(), and close() functions.

1. Opening a File

The first step in working with a file is to open it using the built-in open() function. This function returns a file object, which provides methods to read, write, and manipulate the file.

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

Modes for Opening a File:

• "r": Read (default mode). Opens the file for reading. If the file doesn’t exist, it raises an error.
• "w": Write. Opens the file for writing. If the file already exists, it overwrites it.
• "a": Append. Opens the file for appending. If the file doesn’t exist, it creates a new file.
• "b": Binary mode. Reads or writes the file in binary mode (e.g., "rb", "wb").
• "x": Exclusive creation. Creates a new file, but raises an error if the file already exists.
• "t": Text mode (default). Opens the file in text mode (you can specify this explicitly, but it’s the default).

Example:

file = open("example.txt", "r")  # Open a file in read mode

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2. Reading from a File

You can read the content of a file using several methods:

a. read()

The read() method reads the entire content of the file at once.

file = open("example.txt", "r")
content = file.read()  # Reads the entire file
print(content)
file.close()

b. readline()

The readline() method reads one line at a time from the file.

file = open("example.txt", "r")
line1 = file.readline()  # Reads the first line
print(line1)
file.close()

c. readlines()

The readlines() method reads the entire file and returns a list, where each element is a line from the file.

file = open("example.txt", "r")
lines = file.readlines()  # Returns a list of lines
for line in lines:
    print(line)
file.close()

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3. Writing to a File

There are different methods to write to a file, depending on the mode in which the file is opened.

a. write()

The write() method is used to write a string to the file. If the file is in write or append mode, it will write the string to the file.

file = open("example.txt", "w")  # Open in write mode
file.write("Hello, world!\n")
file.close()

b. writelines()

The writelines() method is used to write a list of strings to a file. Each string is written to the file without any newline characters, so you need to manually add \n if required.

lines = ["Line 1\n", "Line 2\n", "Line 3\n"]
file = open("example.txt", "w")
file.writelines(lines)  # Writes a list of strings to the file
file.close()

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4. Closing the File

It’s important to close the file after performing operations on it. This ensures that resources are released and the file is saved properly.

file.close()

However, Python provides a more efficient way to handle file opening and closing using a with statement, which automatically closes the file after the block of code is executed.

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5. Using with Statement (Context Manager)

The with statement simplifies file handling. It ensures that the file is properly closed after the operations, even if an error occurs within the block.

with open("example.txt", "r") as file:
    content = file.read()
    print(content)
# No need to explicitly call file.close()

The file is automatically closed when the code inside the with block finishes executing.

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6. File Modes in Detail

Here’s a summary of the common file modes:

Mode	Description
"r"	Read mode: Opens the file for reading (default mode). Raises an error if the file doesn't exist.
"w"	Write mode: Opens the file for writing. If the file exists, it is overwritten. If the file doesn't exist, it creates a new one.
"a"	Append mode: Opens the file for writing. If the file exists, data is appended to the end. If it doesn’t exist, a new file is created.
"x"	Exclusive creation: Creates a new file. If the file already exists, an error is raised.
"b"	Binary mode: Used for reading/writing binary files (e.g., "rb", "wb").
"t"	Text mode (default): Used for reading/writing text files.

Example of Opening a File in Append Mode:

with open("example.txt", "a") as file:
    file.write("This is a new line appended to the file.\n")

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7. File Operations and Handling Exceptions

It's good practice to handle potential errors when dealing with files, such as when a file doesn't exist or you don’t have permission to access it. You can use try-except blocks for this.

try:
    with open("example.txt", "r") as file:
        content = file.read()
        print(content)
except FileNotFoundError:
    print("The file does not exist.")
except PermissionError:
    print("You do not have permission to read this file.")

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8. Example: Reading, Writing, and Appending to a File

# Writing to a file
with open("example.txt", "w") as file:
    file.write("Hello, Python!\n")
    file.write("This is a file handling example.\n")

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

# Appending to a file
with open("example.txt", "a") as file:
    file.write("Appended line: Learning file handling.\n")

# Reading again to see the changes
with open("example.txt", "r") as file:
    content = file.read()
    print("Updated file content:")
    print(content)

Output:

File content:
Hello, Python!
This is a file handling example.

Updated file content:
Hello, Python!
This is a file handling example.
Appended line: Learning file handling.

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9. Working with Binary Files

You can open and handle binary files (e.g., images, videos, etc.) using the "b" mode. This is useful for non-text files.

Example: Reading and Writing a Binary File

# Writing a binary file
with open("example.bin", "wb") as file:
    file.write(b'\xDE\xAD\xBE\xEF')  # Writing bytes

# Reading a binary file
with open("example.bin", "rb") as file:
    data = file.read()
    print(data)

Output:

b'\xde\xad\xbe\xef'

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10. Working with Directories

Python also allows you to handle directories (create, delete, list files) using the os and shutil modules.

import os

# Create a directory
os.mkdir("new_folder")

# List files in a directory
files = os.listdir(".")
print(files)

# Remove a directory
os.rmdir("new_folder")

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Summary

• Opening a file: Use open() with different modes (r, w, a, b, etc.).
• Reading from a file: Use read(), readline(), or readlines() methods.
• Writing to a file: Use write() or writelines() to write text to a file.
• Closing a file: Always close files after use or use with for automatic closing.
• Error handling: Use try-except blocks to handle potential errors (e.g., FileNotFoundError).
• Binary files: Use "b" mode for binary files.
• Directory operations: Use the os module to create, list, and delete directories.