6.1 Opening and Closing Files

We learn the basic open() function, its various modes, and the importance of the close() method for file management.

To work with a file on disk, the first step is to open it. The built-in `open()` function is the key to this process. It returns a "file object," which is like an intermediary that allows you to read or write data to the physical file.

The open() Function

The `open()` function takes two main arguments: the file path and the mode in which to open it. It is crucial to always close the file with the `close()` method to release system resources and ensure any changes are properly saved to disk.

File Modes

`"r"` (Read): Default mode. Opens a file for reading. Raises an error if the file does not exist.
`"w"` (Write): Opens a file for writing. If the file exists, its content is deleted. If it does not exist, a new one is created.
`"a"` (Append): Opens a file for appending to the end. If it does not exist, a new one is created.
`"x"` (Create): Creates a new file. If the file already exists, it raises an error.

You can also add a `"+"` (e.g., `"r+"`, `"w+"`) to allow simultaneous reading and writing.

Tip!

The live editor operates in a temporary environment. The files you create are not permanently stored, but the code is fully functional in a normal Python environment.

# Example of writing, reading, and appending to a file.
# Note: This file is temporary in the live editor.

# 1. Writing to a file (mode "w" - replaces content)
try:
    file_writer = open("my_first_file.txt", "w", encoding="utf-8")
    file_writer.write("This is my first line in a file.\n")
    file_writer.close()
    print("'my_first_file.txt' was created for writing.")
except Exception as e:
    print(f"Write error: {e}")

# 2. Reading from a file (mode "r")
try:
    file_reader = open("my_first_file.txt", "r", encoding="utf-8")
    content = file_reader.read()
    print("\nContent of 'my_first_file.txt':\n" + content)
    file_reader.close()
except FileNotFoundError:
    print("\nError: 'my_first_file.txt' not found.")

# 3. Appending to a file (mode "a")
try:
    file_appender = open("my_first_file.txt", "a", encoding="utf-8")
    file_appender.write("This line was appended to the end.\n")
    file_appender.close()
    print("A new line was appended to the file.")
except Exception as e:
    print(f"Append error: {e}")

# 4. Reading again to confirm
try:
    file_final_reader = open("my_first_file.txt", "r", encoding="utf-8")
    print("\nFinal content of 'my_first_file.txt':")
    for line in file_final_reader:
        print(line.strip())
    file_final_reader.close()
except FileNotFoundError:
    print("Error: 'my_first_file.txt' not found for final read.")

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