CODEWITHSUNDEEP
pythonfile-io
Hunter McMillen
Hunter McMillen

Reputation: 61550

Reading and writing to a file

I have an XML file that contains an illegal character, I am iterating through the file, removing the character from all of the lines and storing the lines in a list. I now want to write those same lines back into the file and overwrite what is already there.

I tried this:

file = open(filename, "r+")
#do stuff

Which is only appending the results to the end of the file, I would like to overwrite the existing file.

And this:

file = open(filename, "r")
#read from the file
file.close()

file = open(filename, "w")
#write to file
file.close()

This gives me a Bad File Descriptor error.

How can i read and write to the same file?

Thanks

Upvotes: 0

Views: 1004

Answers (2)

JAB
JAB

Reputation: 21089

The reason you're appending to the end of the file the whole time is that you need to seek to the beginning of the file to write your lines out.

with open(filename, "r+") as file:
    lines = file.readlines()

    lines = [line.replace(bad_character, '') for line in lines]

    file.seek(0)
    file.writelines(lines)
    file.truncate()         # Will get rid of any excess characters left at the end of the file due to the length of your new file being shorter than the old one, as you've removed characters.

(Decided to just use the context manager syntax myself.)

Upvotes: 0

utdemir
utdemir

Reputation: 27266

You could re-write the lines list with writelines function.

with open(filename, "r") as f:

    lines = f.readlines()

#edit lines here

with open(filename, "w") as f:

    f.writelines(lines)

Upvotes: 2

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