Python Read, Write, Create and Delete Files

The mode passed to open() decides what you can do and what happens to an existing file:

Add "b" for binary ("rb", "wb") and "t" for text, which is the default.

"w" is the dangerous one: the existing contents are discarded the moment the file is opened, before you write anything. When a file must not be replaced, for example a survey record for a specific date, use "x" and handle FileExistsError. When adding to a history, use "a".

Text files are stored as bytes, and an encoding says how characters map to bytes. If you don't specify one, Python uses a platform default, which may differ between Windows and Linux, so a file written on one machine can be misread on another:

with open("species.txt", "w", encoding="utf-8") as file:
    file.write("Fauvette à tête noire\n")

Always pass encoding="utf-8" for text unless you know the file uses something else. Reading a file with the wrong encoding raises UnicodeDecodeError or, worse, silently shows garbled characters. Python 3.15 is expected to make UTF-8 the default everywhere, but stating it explicitly works on every version.

Images, audio, PDFs and other non-text files must be opened in binary mode, which reads and writes bytes without any decoding: with open("nest.jpg", "rb") as file: data = file.read(). Binary mode doesn't accept an encoding argument.

Opening a file inside a with statement makes Python close it automatically when the block ends, including when an exception is raised. Closing matters: written data may sit in a buffer until the file is closed, and operating systems limit how many files a program can have open.

with open("nest_log.txt", "a", encoding="utf-8") as log:
    log.write("Robin: 4 eggs\n")
    log.write("Wren: 6 eggs\n")
# closed and flushed here

Keep the file open for all the related writes, rather than reopening it for every line. print("Robin: 4 eggs", file=log) is a handy alternative to write() because it adds the newline for you. For small files, Path.write_text() and Path.read_text() open, write or read, and close in one call. The context managers lesson explains how with works underneath.

Path.unlink() deletes a file; os.remove() does the same. Deletion is permanent: Python doesn't use the recycle bin.

from pathlib import Path
draft = Path("draft_notes.txt")
draft.unlink(missing_ok=True)     # no error if already gone (Python 3.8+)

Without missing_ok=True, deleting a missing file raises FileNotFoundError. Deleting a folder needs Path.rmdir() (empty folders only) or shutil.rmtree() (everything inside, with no confirmation).

Before deleting, make sure the path is the one you intend: print it, check path.is_file(), and never build deletion paths from unchecked user input. Programs that clean up their own temporary files are safer using the tempfile module, which creates files in a dedicated temporary folder and removes them automatically.

Task: use a disposable observation file to demonstrate exclusive creation, reading, appending and removal.

from pathlib import Path

obs = Path("practice_obs.txt")
obs.unlink(missing_ok=True)

with obs.open("x", encoding="utf-8") as f:
    f.write("Blackbird: 2 eggs\n")
with obs.open("a", encoding="utf-8") as f:
    f.write("Blue tit: 9 eggs\n")

lines = obs.read_text(encoding="utf-8").splitlines()
print(lines)                 # ['Blackbird: 2 eggs', 'Blue tit: 9 eggs']
obs.unlink()
print(obs.exists())          # False

splitlines() removes the newline characters, giving clean strings. For the worked check, the mode that refuses to overwrite an existing file is "x": it raises FileExistsError instead.

The documentation for open() lists every mode, and pathlib covers read_text, write_text and unlink. Continue with directory operations and JSON handling. Practise with the Python exercises and Python quiz.