A file that already contains notes can be a place to add another line without losing what’s there. Python’s append mode writes new text at the end, while other modes can create or replace a file.
I’ll explain how the modes differ and show how to append text without replacing what’s already there.
TL;DR: Write a File in Python
Use open() with a context manager, choose w to replace content or a to append, then call write() with a string.
- Use encoding=”utf-8″ for predictable text handling.
- Use x when an existing file must not be overwritten.
- Add \n where each written line should end.
What Does Writing a File in Python Mean?
A file object is the stream Python uses to access a file. In text mode, the stream accepts strings for writing.
For reading saved contents later, see the Python file reading guide.
| Mode | What it does | Use it when |
|---|---|---|
| w | Creates a missing file or clears an existing file before writing | You intend to replace the old contents |
| a | Creates a missing file or writes at the end | You need to preserve existing text |
| x | Creates a new file and raises FileExistsError if it exists | Replacing a file would be unsafe |
Choose the mode before writing. The + flag adds reading to a mode, but a write-only stream is simpler when the task only saves text. For reading the saved contents later, see the Python file reading guide.
How to Write a File in Python Step by Step
Open the path with the intended mode, write strings, and let the context manager close the file. A with block also closes it when an error occurs.
Step 1: Open a text file with an encoding
The filename is relative to the process’s current working directory. This example selects w because it creates or replaces the sample file.
from pathlib import Path
path = Path("notes.txt")
with path.open("w", encoding="utf-8") as file:
file.write("First line\n")
file.write("Second line\n")
Each write() call takes a string. The newline character is part of the string, so it separates the lines when the file is read back.
Step 2: Read back the saved text
After the write block closes, open the same path for reading and print its contents. I ran the example with python3 write_file_demo.py and got:
with path.open(encoding="utf-8") as file:
print(file.read(), end="")
Reading the file back confirms the saved text and its line breaks.
Step 3: Append instead of replacing
Append mode writes at the end, so it preserves text already in the file. Use it for a simple log entry or another record that should follow earlier content.
with open("notes.txt", "a", encoding="utf-8") as file:
file.write("Third line\n")
To write several strings, call writelines() with an iterable of strings. It does not insert line breaks for you, so include \n in each item that should end a line.
lines = ["First\n", "Second\n"]
with open("notes.txt", "w", encoding="utf-8") as file:
file.writelines(lines)
For structured comma-separated records, use Python’s csv module rather than joining values with commas by hand. It handles CSV quoting rules that simple string concatenation does not.
File-Writing Errors and Next Steps
Many surprises come from the selected mode, the file path, or missing line breaks. Check these cases before changing the code.
| Case | Symptom | Fix |
|---|---|---|
| Existing text disappears | w truncates the file when opened | Use a to preserve and extend it, or x to refuse an existing path |
| Lines run together | write() and writelines() do not add separators | Include \n in the strings |
| File appears in the wrong directory | A relative path is resolved from the process working directory | Use Path.cwd() to inspect that directory or pass an explicit path |
A relative filename is resolved from the process’s current working directory, which may differ from the folder containing the script. If you save to a path supplied by a user or built from input, validate that path for your application before opening it.
Set encoding=”utf-8″ when the file must use UTF-8. A read-only destination or missing parent directory raises an operating-system error when opened for writing. Check the path and permissions before retrying.
Conclusion: Choose the File Mode First
A known path and a read-back check make a small file-writing task straightforward to verify. For more file operations, see the guide to printing to a file.
For details on file objects and text modes, see the Python open() documentation and the Python input and output tutorial.
FAQ
These short answers cover common choices when writing a text file in Python.
How do I write text to a file in Python?
Open it with open() in a with block, choose a writing mode such as w, and call write() with a string. Specify encoding=”utf-8″ for text.
Does writelines() add a newline?
No. Include newline characters in the strings when you want each item on its own line.
How do I add text without overwriting a file?
Open the file in append mode, a. It writes new text at the end and leaves existing contents in place.
