Behavior of which readline? GNU readline? Note that it is only one particular implmentation on one particular platform while Python should be as multiplatform as possible / viable.
And what behavior it is? More precisely, what incorrect behavior in Linux would it bring if the condition in
if (!isatty (fileno (sys_stdin)) || !isatty (fileno (sys_stdout)))
rv = PyOS_StdioReadline (sys_stdin, sys_stdout, prompt);
else
rv = (*PyOS_ReadlineFunctionPointer)(sys_stdin, sys_stdout, prompt);
was replaced by `!isatty (fileno (sys_stdin))`?