Python Write/Create Files ✍️

Writing to Files

To write to a file, use the open() function with mode "w" (write) or "a" (append).

📓 Analogy: The Notebook

- Append ("a"): Like turning to a new page in your notebook and continuing to write. The old notes stay there.
- Write ("w"): Like erasing the ENTIRE notebook and starting fresh on page 1. Be careful!

✨ Append ("a")

Appends content to the end of the file. Does NOT delete existing content.

python

with open("demofile.txt", "a") as f:
    f.write("This text is appended.")

🔄 Overwrite ("w")

Overwrites the entire file. All previous content is lost!

python

with open("demofile.txt", "w") as f:
    f.write("I have deleted the content!")

🎯 Real-World Application: Exporting Data

Writing user data to a CSV file for Excel.

python

users = ["Alice,25", "Bob,30", "Charlie,35"]

with open("users.csv", "w") as f:
    f.write("Name,Age\n") # Header
    for user in users:
        f.write(user + "\n")

🆕 Create New File ("x")

Creates a new file. Returns an error if the file already exists.

python

try:
    with open("myfile.txt", "x") as f:
        f.write("New file created!")
except FileExistsError:
    print("File already exists.")

💡 Writing Lists

You can write a list of strings to a file using writelines().

python

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