File Operations

Python provides several built-in functions to perform basic file operations, such as opening, reading, writing, and closing files.

1. Opening a File:

   • Use the open() function to open a file. The open() function returns a file object, which allows you to interact with the file.
   • Syntax:

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

   • Common modes include:
     • 'r': Read (default mode)
     • 'w': Write (creates a new file or truncates an existing file)
     • 'a': Append (writes to the end of the file without truncating)
     • 'b': Binary mode (used with other modes for binary files)

2. Reading a File:

   • read(): Reads the entire file content as a string.
   • readline(): Reads a single line from the file.
   • readlines(): Reads all lines and returns them as a list.
   • Example:

     file = open("example.txt", "r")
     content = file.read()  # Reads entire file
     first_line = file.readline()  # Reads first line
     all_lines = file.readlines()  # Reads all lines as a list
     file.close()
     

3. Writing to a File:

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

     file = open("example.txt", "w")
     file.write("Hello, World!\n")
     lines = ["Line 1\n", "Line 2\n", "Line 3\n"]
     file.writelines(lines)
     file.close()
     

4. Appending to a File:

   • Use 'a' mode to append content to the end of the file without truncating it.
   • Example:

     file = open("example.txt", "a")
     file.write("This line is appended.\n")
     file.close()
     

5. Closing a File:

   • Always close the file after performing operations to free system resources.
   • Example:

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

File Handling Using with Statement

Using the with statement is the preferred way to handle files in Python. It ensures that the file is properly closed after its suite finishes, even if an exception occurs.

• Example:

  with open("example.txt", "r") as file:
      content = file.read()
  # The file is automatically closed after the block
  

Working with Binary Files

To work with binary files, use the 'b' mode along with the other modes. This is essential for non-text files like images, videos, and executables.

• Example:

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

File Positioning

You can control the file's current position using seek() and check it with tell().

• seek(offset, whence): Moves the file pointer to a specific position.
  • offset: Number of bytes to move.
  • whence: Starting point (0 = start, 1 = current position, 2 = end).
  • Example:

    file = open("example.txt", "r")
    file.seek(0)  # Move to the start of the file
    

• tell(): Returns the current file position.
  • Example:

    position = file.tell()  # Get current file position
    

Handling File Exceptions

File handling can raise exceptions, such as FileNotFoundError or IOError. It's important to handle these exceptions to prevent the program from crashing.

• Example:

  try:
      file = open("nonexistent.txt", "r")
  except FileNotFoundError:
      print("File not found.")
  finally:
      file.close()