Question

I want to read bytes from a file and then write those bytes to another file, and save that file.

How do I do this?

Answer 1

Here’s how to do it with the basic file operations in Python. This opens one file, reads the data into memory, then opens the second file and writes it out.

in_file = open("in-file", "rb") # opening for [r]eading as [b]inary
data = in_file.read() # if you only wanted to read 512 bytes, do .read(512)
in_file.close()

out_file = open("out-file", "wb") # open for [w]riting as [b]inary
out_file.write(data)
out_file.close()

We can do this more succinctly by using the with keyboard to handle closing the file.

with open("in-file", "rb") as in_file, open("out-file", "wb") as out_file:
    out_file.write(in_file.read())

If you don’t want to store the entire file in memory, you can transfer it in pieces.

chunk_size = 4096 # 4 KiB

with open("in-file", "rb") as in_file, open("out-file", "wb") as out_file:
    while True:
        chunk = in_file.read(chunk_size)
            
        if chunk == b"":
            break # end of file
            
        out_file.write(chunk)