How to delete only the content of file in python

Question

I have a temporary file with some content and a python script generating some output to this file. I want this to repeat N times, so I need to reuse that file (actually array of files). I'm deleting the whole content, so the temp file will be empty in the next cycle. For deleting content I use this code:

def deleteContent(pfile):

    pfile.seek(0)
    pfile.truncate()
    pfile.seek(0) # I believe this seek is redundant

    return pfile

tempFile=deleteContent(tempFile)

My question is: Is there any other (better, shorter or safer) way to delete the whole content without actually deleting the temp file from disk?

Something like tempFile.truncateAll()?

Answer 1

How to delete only the content of file in python

There is several ways of set the logical size of a file to 0, depending how you access that file:

To empty an open file:

def deleteContent(pfile):
    pfile.seek(0)
    pfile.truncate()

---

To empty a open file whose file descriptor is known:

def deleteContent(fd):
    os.ftruncate(fd, 0)
    os.lseek(fd, 0, os.SEEK_SET)

---

To empty a closed file (whose name is known)

def deleteContent(fName):
    with open(fName, "w"):
        pass

---

---

I have a temporary file with some content [...] I need to reuse that file

That being said, in the general case it is probably not efficient nor desirable to reuse a temporary file. Unless you have very specific needs, you should think about using tempfile.TemporaryFile and a context manager to almost transparently create/use/delete your temporary files:

import tempfile

with tempfile.TemporaryFile() as temp:
     # do whatever you want with `temp`

# <- `tempfile` guarantees the file being both closed *and* deleted
#     on exit of the context manager