Python with Statement (Opening Files Safely)

In the last two lessons, every file you opened needed a matching close(). Forget it once, or let an error skip it, and strange bugs follow. The Python with statement fixes this: it opens a file and guarantees it gets closed, no matter how the block ends. It's the way professional Python code opens files, and after this lesson it'll be your way too.

Why does closing a file matter?

When you write to a file, Python doesn't send every character to the disk right away. It collects text in a buffer (a small waiting area in memory) and saves it in batches, because disks are slow. Closing the file flushes the buffer, which means it writes out everything still waiting. Watch what happens before and after close():

notes = open("notes.txt", "w", encoding="utf-8")
notes.write("Buy milk\n")

reader = open("notes.txt", encoding="utf-8")
print(repr(reader.read()))
reader.close()

notes.close()

reader = open("notes.txt", encoding="utf-8")
print(repr(reader.read()))
reader.close()

''
'Buy milk\n'

Before close(), the file on disk was still empty. Unclosed files cause other problems too:

• Lost data if the program crashes before the buffer is saved.
• Locked files: on Windows, another program may be unable to rename or delete a file you left open.
• Running out of file handles: operating systems limit how many files one program can have open at once, which matters in long-running programs like web servers.

What is the with statement in Python?

The with statement runs an indented block of code inside a "setup and cleanup" wrapper. For files, the setup is opening the file and the cleanup is closing it. Here's the pattern:

with open("guests.txt", encoding="utf-8") as file:
    content = file.read()

print(content)
print("Closed?", file.closed)

Alice
Bob
Chloe
Diego

Closed? True

Let's break down the first line:

• with starts the statement.
• open("guests.txt", encoding="utf-8") opens the file, exactly as before.
• as file stores the file object in a variable named file.
• The colon and the indented block are the code that uses the file.

As soon as the indented block ends, Python closes the file for you. The closed attribute proves it. (guests.txt is the four-name file from How to Read Files in Python.)

How do you write to a file with the with statement?

Every mode works the same way. Here we append a diary entry:

with open("diary.txt", "a", encoding="utf-8") as diary:
    diary.write("Went for a run in the park.\n")
    diary.write("Tried a new pasta recipe.\n")

with open("diary.txt", encoding="utf-8") as diary:
    print(diary.read())

Went for a run in the park.
Tried a new pasta recipe.

Compare that with the old way: no close() lines, and the indentation shows at a glance which code uses the file.

Does with close the file even when there's an error?

Yes, and that's its biggest advantage. Below, int() fails because the first line of the guest list is a name, not a number. The error jumps straight out of the block, yet the file is still closed:

try:
    with open("guests.txt", encoding="utf-8") as file:
        first_line = file.readline()
        number = int(first_line)
        print("This line never runs")
except ValueError:
    print("The first line isn't a number!")

print("Closed?", file.closed)

The first line isn't a number!
Closed? True

Without with, you'd need a try/finally block (from Python try except) to get the same safety:

file = open("guests.txt", encoding="utf-8")
try:
    content = file.read()
finally:
    file.close()

Both versions behave the same, but the with version is shorter and impossible to get wrong.

How do you open multiple files in one with statement?

Separate them with commas. Both files are closed when the block ends. This example turns a guest list into name badges:

with open("guests.txt", encoding="utf-8") as guests, open("badges.txt", "w", encoding="utf-8") as badges:
    for line in guests:
        badges.write(f"HELLO, my name is {line.strip()}\n")

with open("badges.txt", encoding="utf-8") as badges:
    print(badges.read())

HELLO, my name is Alice
HELLO, my name is Bob
HELLO, my name is Chloe
HELLO, my name is Diego

When the line gets long, Python 3.10 and newer let you wrap the files in parentheses, one per line:

with (
    open("guests.txt", encoding="utf-8") as guests,
    open("badges.txt", "w", encoding="utf-8") as badges,
):
    for line in guests:
        badges.write(f"Welcome, {line.strip()}!\n")

with open("badges.txt", encoding="utf-8") as badges:
    print(badges.readline().strip())

Welcome, Alice!

Real-world example: building an RSVP list

You invited friends to a party and saved their replies in rsvp.txt:

Alice,yes
Bob,no
Chloe,yes
Diego,maybe
Emma,yes

This program reads the replies and writes only the confirmed guests to a new file for the caterer:

confirmed = 0

with open("rsvp.txt", encoding="utf-8") as replies, open("confirmed.txt", "w", encoding="utf-8") as output:
    for line in replies:
        name, answer = line.strip().split(",")
        if answer == "yes":
            output.write(name + "\n")
            confirmed += 1

print(f"{confirmed} guests confirmed. Plates to order: {confirmed + 1}")

with open("confirmed.txt", encoding="utf-8") as output:
    print(output.read())

3 guests confirmed. Plates to order: 4
Alice
Chloe
Emma

The + 1 is a plate for the host. Notice that the program reads confirmed.txt only after the first with block has closed it, so all the names have been saved.

with and context managers

A file object works with with because it's a context manager: an object that knows how to set something up when the block starts and clean it up when the block ends. Files aren't the only ones. Database connections, network connections and locks that stop two parts of a program from changing the same data at once are all commonly used with with.

You can even write your own context managers, for example a timer that measures how long a block takes. You'll learn how in Python Context Managers.

Common mistakes with the with statement

1. Using the file after the block ends

with open("guests.txt", encoding="utf-8") as file:
    first = file.readline()

second = file.readline()

ValueError: I/O operation on closed file.

Keep every line that reads or writes the file inside the indented block, or save what you need in a variable first.

2. Forgetting the colon or the indentation

Like if and for, a with line must end with :, and the code that uses the file must be indented beneath it.

3. Calling close() inside with

It isn't an error, but it's unnecessary. Let with do the closing.

4. Reading a file you're still writing in the same block

Text you wrote may still be in the buffer. Finish writing, let the block end, then open the file again to read it, as the RSVP example does.

Practice exercise

with open("guests.txt", encoding="utf-8") as guests, open("seating.txt", "w", encoding="utf-8") as seating:
    table = 1
    for line in guests:
        seating.write(f"Table {table}: {line.strip()}\n")
        table += 1

with open("seating.txt", encoding="utf-8") as seating:
    print(seating.read())

Table 1: Alice
Table 2: Bob
Table 3: Chloe
Table 4: Diego

What's next?

You can now read and write text files safely. Many real files hold tables of data, like spreadsheets exported from Excel. Next, learn how to work with CSV files in Python.