Take the "Head" of every file in a directory?

I am working with large files, and my question here is two-fold.

1. Bash - For testing purposes, I would like to iterate over every file in a given directory, taking the Head of each file (say Head10000), and be left with a cut-down version of each. Either in thesame directory or another it doesn't matter a whole lot, though Isuppose the same would be preferred.

2. Python3 - How can I do this programmatically? I imagine I need to use the os module?