YanoSec / Code
Python module self-review case.
Review card. Do not save this as a .py file and do not run it.

Supplied source bytes, hex: 41 42
That is two bytes.

Line A: def copy_out(source, dest):
Line B:     with open(source, "rb") as handle:
Line C:         data = handle.read()
Line D:     print(len(data))
Line E:     with open(dest, "wb") as handle:
Line F:         handle.write(data)

Predicted display from line D, for the supplied two bytes: 2
Line D prints a count. It does not delete source.
Lines E and F write those bytes into dest. That changes dest.
Do not run the card to discover the write. The mode wb is the evidence.
Rubric: name the input, the printed count, and the modifying lines.
State that a comment or a harmless filename would not have made line E safe.