[python] How to erase the file contents of text file in Python?

I have text file which I want to erase in Python. How do I do that?

Not a complete answer more of an extension to ondra's answer

When using truncate() ( my preferred method ) make sure your cursor is at the required position. When a new file is opened for reading - open('FILE_NAME','r') it's cursor is at 0 by default. But if you have parsed the file within your code, make sure to point at the beginning of the file again i.e truncate(0) By default truncate() truncates the contents of a file starting from the current cusror position.

A simple example

You cannot "erase" from a file in-place unless you need to erase the end. Either be content with an overwrite of an "empty" value, or read the parts of the file you care about and write it to another file.

Opening a file in "write" mode clears it, you don't specifically have to write to it:

open("filename", "w").close()

(you should close it as the timing of when the file gets closed automatically may be implementation specific)

Assigning the file pointer to null inside your program will just get rid of that reference to the file. The file's still there. I think the remove() function in the c stdio.h is what you're looking for there. Not sure about Python.

When using with open("myfile.txt", "r+") as my_file:, I get strange zeros in myfile.txt, especially since I am reading the file first. For it to work, I had to first change the pointer of my_file to the beginning of the file with my_file.seek(0). Then I could do my_file.truncate() to clear the file.

If security is important to you then opening the file for writing and closing it again will not be enough. At least some of the information will still be on the storage device and could be found, for example, by using a disc recovery utility.

Suppose, for example, the file you're erasing contains production passwords and needs to be deleted immediately after the present operation is complete.

Zero-filling the file once you've finished using it helps ensure the sensitive information is destroyed.

On a recent project we used the following code, which works well for small text files. It overwrites the existing contents with lines of zeros.

import os

def destroy_password_file(password_filename):
    with open(password_filename) as password_file:
        text = password_file.read()
    lentext = len(text)
    zero_fill_line_length = 40
    zero_fill = ['0' * zero_fill_line_length
                      for _
                      in range(lentext // zero_fill_line_length + 1)]
    zero_fill = os.linesep.join(zero_fill)
    with open(password_filename, 'w') as password_file:
        password_file.write(zero_fill)

Note that zero-filling will not guarantee your security. If you're really concerned, you'd be best to zero-fill and use a specialist utility like File Shredder or CCleaner to wipe clean the 'empty' space on your drive.

You have to overwrite the file. In C++:

#include <fstream>

std::ofstream("test.txt", std::ios::out).close();

Writing and Reading file content

def writeTempFile(text = ''):
    filePath = "/temp/file1.txt"
    if not text:                      # If blank return file content
        f = open(filePath, "r")
        slug = f.read()
        return slug
    else:
        f = open(filePath, "a") # Create a blank file
        f.seek(0)  # sets  point at the beginning of the file
        f.truncate()  # Clear previous content
        f.write(text) # Write file
        f.close() # Close file
        return text

It Worked for me

From user @jamylak an alternative form of open("filename","w").close() is

with open('filename.txt','w'): pass

You can also use this (based on a few of the above answers):

file = open('filename.txt', 'w')
file.close()

of course this is a really bad way to clear a file because it requires so many lines of code, but I just wrote this to show you that it can be done in this method too.

happy coding!

Since text files are sequential, you can't directly erase data on them. Your options are:

• The most common way is to create a new file. Read from the original file and write everything on the new file, except the part you want to erase. When all the file has been written, delete the old file and rename the new file so it has the original name.
• You can also truncate and rewrite the entire file from the point you want to change onwards. Seek to point you want to change, and read the rest of file to memory. Seek back to the same point, truncate the file, and write back the contents without the part you want to erase.
• Another simple option is to overwrite the data with another data of same length. For that, seek to the exact position and write the new data. The limitation is that it must have exact same length.

Look at the seek/truncate function/method to implement any of the ideas above. Both Python and C have those functions.