hello, I want to change n bytes of a binary file

[Fredrik Lundh]

"could ildg" wrote:

> > so how can I do the binary stuff?
>
> 8-bit strings contain bytes.
>
> > I want a encrypt function like below:
> > def encrypt(filename,n):
>
> f = open(filename,"rb+")
>
> > a=f.read(n)
>
> b = encrypt(a)

^^^^^^^^Thank you~~,but where is the encrypt defined?

oh, I though you asked how to update the first n bytes of a
binary file.

if you want to XOR the bytes, you can do something like:

    import array
    b = array.array("B", a)
    for i in range(len(b)):
        b[i] = b[i] ^ 255
    b = b.tostring()

or

    b = "".join([chr(ord(c) ^ 255) for c in a])

or some variation thereof.

</F>