Why file.write() is appending in r mode in Python?-CodePudding

Assume I have a file content.txt, with the content Ex nihilo nihil fit. I am willing to replace it with Ex nihilo nihil est. The code is:

with open("content.txt", "r ") as f:
    content = f.read()
    content = content.replace("fit", "est")
    print(content)
    f.write(content)
    f.close()

After that, the content of the file becomes:

Ex nihilo nihil fit
Ex nihilo nihil est

Why? The only thing I need is Ex nihilo nihil est. What is the correct code?

CodePudding user response：

r opens the file and puts a pointer at the first byte. When you use f.read() the pointer moves to the end of the file, so when you try to write it starts at the end of the file. To move back to the start (so you can override), use f.seek(0):

with open("text.txt", "r ") as f:
    content = f.read()
    content = content.replace("fit", "est")
    print(content)
    f.seek(0)
    f.write(content)
    f.close()

CodePudding user response：

At the moment you are appending the modified content to the file.

What you want is to clear the content first. You can use seek and truncate for that.

with open("content.txt", "r ") as f:
    content = f.read()
    content = content.replace("fit", "est")
    print(content)
    f.seek(0)  # move to first byte
    f.truncate()  # delete content
    f.write(content)

CodePudding user response：

Try the code below if you want to replace a string in a .txt file :

with open("content.txt", 'r') as file :
    content = file.read()

content = content.replace('fit', 'est')

with open("content.txt", 'w') as file:
    file.write(content)