Python: Working with Files

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1. What is File Handling?

• File handling refers to reading from and writing to files in Python.
• Files are used to store data persistently, even after the program ends.
• Python provides built-in functions and methods to work with files.

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2. Opening a File

• Use the open() function to open a file.
• Syntax: open(filename, mode)
• Modes:
  • "r" : Read mode (default). Opens the file for reading.
  • "w" : Write mode. Opens the file for writing (creates a new file or overwrites an existing file).
  • "a" : Append mode. Opens the file for appending (writes data to the end of the file).
  • "x" : Exclusive creation mode. Creates a new file but raises an error if the file already exists.
  • "b" : Binary mode (e.g., "rb", "wb").
  • "+" : Read and write mode (e.g., "r+", "w+").

file = open("example.txt", "r")

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3. Closing a File

• Always close a file after working with it using the close() method.
• This releases system resources and ensures data is properly saved.

file = open("example.txt", "r")
# Perform file operations
file.close()

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4. Using with Statement

• The with statement automatically closes the file after the block of code is executed.
• It is the recommended way to work with files.

with open("example.txt", "r") as file:
    # Perform file operations
    content = file.read()

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5. Reading from a File

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1. read()

• Reads the entire content of the file as a string.

with open("example.txt", "r") as file:
    content = file.read()
    print(content)

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2. readline()

• Reads a single line from the file.

with open("example.txt", "r") as file:
    line = file.readline()
    print(line)

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3. readlines()

• Reads all lines from the file and returns them as a list.

with open("example.txt", "r") as file:
    lines = file.readlines()
    for line in lines:
        print(line.strip())  # Remove newline characters

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6. Writing to a File

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1. write()

• Writes a string to the file.

with open("example.txt", "w") as file:
    file.write("Hello, World!\n")
    file.write("This is a new line.")

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2. writelines()

• Writes a list of strings to the file.

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

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7. Appending to a File

• Use the "a" mode to append data to the end of a file.

with open("example.txt", "a") as file:
    file.write("This is appended text.\n")

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8. Working with Binary Files

• Use the "b" mode to read or write binary data (e.g., images, videos).

with open("image.png", "rb") as file:
    binary_data = file.read()

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9. File Methods and Attributes

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1. seek()

• Moves the file pointer to a specific position.

with open("example.txt", "r") as file:
    file.seek(5)  # Move to the 5th byte
    content = file.read()
    print(content)

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2. tell()

• Returns the current position of the file pointer.

with open("example.txt", "r") as file:
    file.read(10)
    position = file.tell()
    print(f"Current position: {position}")

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3. truncate()

• Resizes the file to a specified size (in bytes).

with open("example.txt", "r+") as file:
    file.truncate(10)  # Truncate to 10 bytes

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10. Additional Examples

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1. Reading a File

with open("names.txt", "r") as file:
    names = file.readlines()
    for name in names:
        print(f"Hello, {name.strip()}!")

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2. Writing to a File

names = ["Raj\n", "Ram\n", "Anand\n", "Bala\n"]
with open("names.txt", "w") as file:
    file.writelines(names)

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3. Appending to a File

with open("names.txt", "a") as file:
    file.write("Karthik\n")

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4. Reading and Writing Binary Data

with open("image.png", "rb") as file:
    binary_data = file.read()

with open("copy_image.png", "wb") as file:
    file.write(binary_data)

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11. Best Practices

• Always use the with statement to ensure files are properly closed.
• Handle exceptions (e.g., FileNotFoundError) when working with files.
• Use meaningful file names and organize files in directories.
• Avoid hardcoding file paths; use relative paths or configuration files.

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