Open files safely with context managers

Completed

To work with a file in Python, you first need to open it. Opening a file gives you a file object you can read from or write to. When you're finished, you need to close the file so the operating system can release its resources and any pending writes are saved.

The problem with forgetting to close a file

You can open a file with open() and close it with .close():

file = open("notes.txt", "r")
contents = file.read()
print(contents)
file.close()

The problem is that if an error happens after open() but before .close(), the file stays open—which can lead to lost data, locked files, or resource leaks.

Using the with statement

The safer, more Pythonic way to work with files is the with statement. It uses a feature called a context manager that automatically closes the file when the block finishes—even if an error occurs.

with open("notes.txt", "r") as file:
    contents = file.read()
    print(contents)
# File is automatically closed here

Everything after as is the name you give the file object inside the block. Once the block ends, the file is closed for you.

File modes

The second argument to open() is the mode, which tells Python what you plan to do with the file:

Mode	Meaning
"r"	Read (default). The file must already exist.
"w"	Write. Creates a new file, or overwrites the existing one.
"a"	Append. Adds to the end of the file, or creates it if missing.
"r+"	Read and write.

Pick the mode that matches what you want to do—using the wrong mode is a common cause of accidentally erased files.

A safer default

For the rest of this module, always open files using with. It's the safest pattern and the one you'll see in almost every real Python codebase.