File Reading and Writing

Python allows you to read from and write to text files using the built-in open() function.

This is useful for saving data to a file or loading it back later.

1. Opening a File

Use open(filename, mode) to work with a file.

• "r" = read (default)
• "w" = write (overwrites file)
• "a" = append (adds to the end)
• "x" = create (fails if file already exists)

Always close a file after using it — or better yet, use a with block to handle this automatically.

2. Reading a File

Open a file in "r" mode to read its contents.

Reading a File

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

• The with statement ensures the file closes automatically.
• The read() method loads the entire file into a single string.

3. Writing to a File

Open a file in "w" mode to create or overwrite it.

Writing to a File

with open("note.txt", "w") as file:
    file.write("This is a new line.")

• The "w" mode creates the file or replaces its content.
• Use the write() method to add text to the file.

4. Appending to a File

Open a file in "a" mode to add new content without removing existing data.

Appending to a File

with open("note.txt", "a") as file:
    file.write("\nThis line is added.")

• The "a" mode preserves existing content and writes new text at the end.

Summary

Mode	Description
"r"	Read only mode
"w"	Write mode (overwrites file)
"a"	Append mode (adds to end of file)
"x"	Create mode, error if it exists

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