When iterating on sys.stdin lines, '\r\n' and '\n' are handled correctly, but '\r' is not handled, though it is documented that it should be supported.

Example code:
import sys

for line in sys.stdin:
    print(repr(line))

Results in Python 3.8.9:
$ echo -e 'line1\nline2\nline3' | python3 linetest.py 
'line1\n'
'line2\n'
'line3\n'

$ echo -e 'line1\r\nline2\r\nline3' | python3 linetest.py 
'line1\r\n'
'line2\r\n'
'line3\n'

$ echo -e 'line1\rline2\rline3' | python3 linetest.py 
'line1\rline2\rline3\n'