The fact that in IDLE sys.stdin is a idlelib.rpc.RPCProxy  results in programs having different behavior in IDLE and in Command Line mode.

I noticed that when grading many students exercises in IDLE. Things like:

sys.stdin.readlines()

just don´t exists in IDLE, but are fully operational in Command Line mode.

In Command Line mode, sys.stdin is a file.

This is expected, as the manual (27.1) says that sys.stdin (and stdout and stderrr) are "File objects corresponding to the interpreter’s standard input"

There are also other "quirks".

I fell that is really strange that stdin has different behavior for the same program.