[Python-Dev] Suggested API change to PyOS_InputHook (original) (raw)

Michael Abbott michael at araneidae.co.uk
Mon Jun 23 09:02:52 CEST 2008

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I have a problem with the PyOS_InputHook() API as implemented by Modules/readline.c: there is no way to communicate any interruption seen while waiting at the keyboard back to the process actually reading the line.

I have solved this in my own application by creating a new module which reimplements the call_readline function and which has the following patch to readline_until_enter_or_signal():

                    FD_SET(fileno(rl_instream), &selectset);
                    /* select resets selectset if no input was available */
                    has_input = select(fileno(rl_instream) + 1, &selectset,
                                       NULL, NULL, &timeout);

                  if(PyOS_InputHook) PyOS_InputHook();

```
       if (call_readline_InputHook  &&
```

           call_readline_InputHook(fileno(rl_instream)))

```
       {
```
```
           has_input = -1;
```
```
           PyErr_SetInterrupt();
```
```
           break;
```

       }
          }

          if(has_input > 0) {
                  rl_callback_read_char();
          }

```
          else if (errno == EINTR) {
```

   else if (errno == EINTR || has_input < 0) {
                  int s;

#ifdef WITH_THREAD PyEval_RestoreThread(_PyOS_ReadlineTState);

(I'm sorry, this isn't a proper patch, but hopefully if you've read this far you can figure out where it applies.)

Here I've replaced PyOS_InputHook with effective type signature None->None with my own call_readline_InputHook which takes a file descriptor and returns a boolean, returning True iff an interrupt occurred. The file descriptor argument is a triviality, but the boolean return code is clearly crucial.

Now, I don't know how this change might fit into mainstream Python, but I think there is a case for making this change. If the incompatibility was acceptable it would be better to change the signature of PyOS_InputHook (I declared my own variable call_readline_InputHook just to avoid accidents).
I've checked the current svn trunk, and this change remains applicable.

Please CC me in any replies: I am quite literally unable to cope with the volume of traffic that a subscription to python-dev will give me.

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