Micropython automatically converting stdin carriage returns to newlines?

[sandyscott]

I was looking to modify some terminal code (specifically, aiorepl)to make it work nicely with windows clients and encountered this issue.

When I press enter in a windows terminal, MicroPython (v1.19.1 on a Raspberry Pi Pico) appears to recieve 2 linefeed characters (0x0A + 0x0A) instead of a carriage return then a linefeed (0x0D + 0x0A).

Code:

import sys

while(True):
    #input = sys.stdin
    b = sys.stdin.read(1)
    sys.stdout.write("(" + hex(ord(b)) + ")")

Run the code, connect to port using a modified PuTTY configured to send a CRLF, hit enter and you get:

I get similar results when using the Thonny Shell or the REPL shell included in the Micropython plugin for PyCharm.

Am I doing something wrong here or is this a quirk (or bug) with MicroPython?

[dpgeorge]

Yes, MicroPython translates \r to \n (and I think this even follows how CPython works).

You can try using sys.stdin.buffer.read(1), that will not do any translation.

[sandyscott]

OK, thank you. I couldn't find much in the official documentation until I found PEP 278 – Universal Newline Support. I have submitted a PR for aiorepl which uses .buffer.read(), but having seen that PEP I'll see I can simplify it and stick with the standard behaviour.

[sandyscott]

New, much simpler PR: micropython/micropython-lib#560