How to open a file for both reading and writing?

python

file-modes

best-practices

data-structures

byAlex Kataev·Oct 4, 2024

In Python, opening a file for both reading and writing is achieved using the "r+" mode with open(). This facilitates a two-way communication with your file, enabling you to simultaneously read the existing text and write new content.

A concise example is as follows:

with open('example.txt', 'r+') as file:
    file.write('Secret sauce recipe')
    file.seek(0) # Go back to start, let's read that recipe again!
    print(file.read()) # Mmm...secret sauce!

Remember to use seek(0) after writing, since it moves you back to the start of the file, making it ready for reading.

File modes in detail

Understanding file modes in Python is like mastering your toolbox. Each file mode is a specialized tool. Knowing which one to pick up at the right moment can make your task infinitely easier.

Wiping it all with "w+"

Sometimes, we just need a fresh start. That's where "w+" mode comes in, like a data bulldozer. It clears the file before writing, offering you a blank canvas to splash your bits and bytes onto. Use it with caution, as it has a reputation for data annihilation.

with open('example.txt', 'w+') as file:
    file.write('Tabs over spaces, fight me!')
    file.seek(0)
    print(file.read())  # Incoming coding war!

Binary mode and Windows

Working with binary files? Remember to add 'b' to your mode string, like a secret handshake with Windows. So it's 'r+b' to the rescue, to keep those pesky newline translations at bay.

`truncate()`: The surgical strike

The truncate() method is your surgical scalpel, trimming away any extra fat from your file. After a write operation, it discards all unnecessary data, keeping your file in shape.

with open('example.txt', 'r+') as file:
    file.write('Eat. Sleep. Code.')
    file.truncate()  # Truncate any extra fat, coder-style! 🍕 -> 🥦

Now you have clean and organized files, just like your diet after a New Year's resolution.

Choosing the right tool for the job

The file modes in Python are like tools in a toolkit. Picking the right one at the right time makes your coding life easier. Always remember to choose "r+" when you need to jog through the file, read a bit, craft some text, and insert it without losing any data along the way.

Append after inspection

Sometimes, you need to inspect the file before adding to it. Here's how to do it like a pro:

with open('example.txt', 'r+') as file:
    existing_content = file.read() # Peeking at secrets
    file.seek(0, 2)  # Seek to the end of file like a pirate seeking treasure 💎
    file.write('\nAnother day, another bug.') # This line is for all the programmers out there!