Correct way to write line to file?

python

file-operations

best-practices

try-except-blocks

byNikita Barsukov·Nov 2, 2024

To write a line to a file in Python, open() the file with with using either 'w' mode to create a new file, or 'a' mode to append:

with open('myfile.txt', 'w') as file:
    # "Here's the beef!\n"
    file.write('This is a line.\n')

Remember, it's '\n' that tells Python to move to a new line after each write. This technique is a reliable trooper, automatically ensuring file closures and managing any unexpected hiccups.

File modes: Choose your weapon

Files can be opened in different modes, determining how you interact with them:

'w': Tyson punch mode. It overwrites the entire file with your brilliant prose or creates a smart new file for you.
'a': Stealth mode. Adds new content invisibly at the very end of your existing file.
'x': Paranoid mode. Creates a secure new file and goes ballistic with an error if file already exists.
'+': Inspector Gadget mode. Lets you both read and write into one file.

Newline character: Cross-platform diplomat

Use '\n' for newlines to ensure cross-platform compatibility. Python's open() kindly converts '\n' to the appropriate platform-specific end-of-line sequence. However, to tell Python to knock off this convenient behavior, set newline='':

with open('myfile.txt', 'w', newline='') as file:
    # "Another steak on the barbie!\n"
    file.write('Another line.\n')

Beware the deceptive os.linesep as it can cause unexpected line breaks on some platforms. It's the double-agent of newline characters.

The print function: For the less keyboard-happy

In Python 3, if you prefer to delegate newlines to a higher power, you can enlist the help of print():

with open('myfile.txt', 'a') as f:
    # The easy life:
    print("hi there", file=f)

File operations: Unpredictable dragons

File operations can be like wrestling a dragon—you never know when you'll encounter problems like a disk running full, permissions slip-ups, or missing directories. Python's try-except blocks can help you tackle these beasts gracefully:

try:
    with open('myfile.txt', 'w') as file:
        # "Hope it works this time...\n"
        file.write('Exception handling is important.\n')
except IOError as e:
    # "Uh-oh! Houston, we have a problem: {e.strerror}\n"
    print(f'An error occurred: {e.strerror}')

This approach lets your program either pick itself up and keep going or go down in a blaze of grace when a file I/O error is encountered.

Efficiency: The green way

Just like 'reduce, reuse, recycle' helps Earth, sparing use of resources helps your program. With the with statement, Python automatically closes the file once the code block is safely executed.

Remember, Python embraces freedom—"There's more than one way to do it". So Python gives you all the tools:

write(): For times when you need absolute control.
print(): For those that like their code easy to read and their newlines easy to add.
writelines(): For times when you embody ambition and need to tackle a entire sequence of strings.