Reading a file and then overwriting it in Python

Question

I've been trying to read a file and then overwrite it with some updated data. I've tried doing it like this:

#Created filename.txt with some data
with open('filename.txt', 'r+') as f:
    data = f.read()
    new_data = process(data)  # data is being changed
    f.seek(0)
    f.write(new_data)

For some reason, it doesn't overwrite the file and the content of it stays the same.

Answer 1

Truncate the file after seeking to the front. That will remove all of the existing data.

>>> open('deleteme', 'w').write('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa')
>>> f = open('deleteme', 'r+')
>>> f.read()
'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'
>>> f.seek(0)
>>> f.truncate()
>>> f.write('bbb')
>>> f.close()
>>> open('deleteme').read()
'bbb'
>>>