slicing the end of a string in a list

[P Boy]

I had some issues while ago trying to open a large binary file.

Anyway, from file() man page:

If mode is omitted, it defaults to 'r'. When opening a binary file, you
should append 'b' to the mode value for improved portability. (It's
useful even on systems which don't treat binary and text files
differently, where it serves as documentation.) The optional bufsize
argument specifies the file's desired buffer size: 0 means unbuffered,
1 means line buffered, any other positive value means use a buffer of
(approximately) that size. A negative bufsize means to use the system
default, which is usually line buffered for tty devices and fully
buffered for other files. If omitted, the system default is used.2.3