Continuing the recent debate about what is appropriate to the interactive prompt printing, and the wide agreement that whatever we decide, users might think otherwise, I've written up a patch to have the user control via a function in __builtin__ the way things are printed at the prompt. This is not patches@python level stuff for two reasons:
1. I'm not sure what to call this function. Currently, I call it __print_expr__, but I'm not sure it's a good name
2. I haven't yet supplied a default in __builtin__, so the user *must* override this. This is unacceptable, of course.
I'd just like people to tell me if they think this is worth while, and if there is anything I missed.
*** ../python/dist/src/Python/ceval.c Fri Mar 31 04:42:47 2000 --- Python/ceval.c Sat Apr 29 03:55:36 2000 *************** *** 1014,1047 **** case PRINT_EXPR: v = POP(); ! /* Print value except if None */ ! /* After printing, also assign to '_' */ ! /* Before, set '_' to None to avoid recursion */ ! if (v != Py_None && ! (err = PyDict_SetItemString( ! f->f_builtins, "_", Py_None)) == 0) { ! err = Py_FlushLine(); ! if (err == 0) { ! x = PySys_GetObject("stdout"); ! if (x == NULL) { ! PyErr_SetString( ! PyExc_RuntimeError, ! "lost sys.stdout"); ! err = -1; ! } ! } ! if (err == 0) ! err = PyFile_WriteObject(v, x, 0); ! if (err == 0) { ! PyFile_SoftSpace(x, 1); ! err = Py_FlushLine(); ! } ! if (err == 0) { ! err = PyDict_SetItemString( ! f->f_builtins, "_", v); ! } } ! Py_DECREF(v); break; case PRINT_ITEM: --- 1014,1035 ---- case PRINT_EXPR: v = POP(); ! x = PyDict_GetItemString(f->f_builtins, ! "__print_expr__"); ! if (x == NULL) { ! PyErr_SetString(PyExc_SystemError, ! "__print_expr__ not found"); ! Py_DECREF(v); ! break; ! } ! t = PyTuple_New(1); ! if (t != NULL) { ! PyTuple_SET_ITEM(t, 0, v); ! w = PyEval_CallObject(x, t); ! Py_XDECREF(w); } ! /*Py_DECREF(x);*/ ! Py_XDECREF(t); break; case PRINT_ITEM:
-- Moshe Zadka mzadka@geocities.com. http://www.oreilly.com/news/prescod_0300.html http://www.linux.org.il -- we put the penguin in .com
Moshe Zadka writes:
- I'm not sure what to call this function. Currently, I call it
__print_expr__, but I'm not sure it's a good name
It's not. ;) How about printresult? Another thing to think about is interface; formatting a result and "printing" it may be different, and you may want to overload them separately in an environment like IDLE. Some people may want to just say:
import sys sys.formatresult = str
I'm inclined to think that level of control may be better left to the application; if one hook is provided as you've described, the application can build different layers as appropriate.
- I haven't yet supplied a default in __builtin__, so the user *must*
override this. This is unacceptable, of course.
You're right! But a default is easy enough to add. I'd put it in sys instead of __builtin__ though.
-Fred
-- Fred L. Drake, Jr. <fdrake at acm.org> Corporation for National Research Initiatives
On Mon, 1 May 2000, Fred L. Drake, Jr. wrote:
It's not. ;) How about printresult?
Hmmmm...better then mine at least.
import sys sys.formatresult = str
And where does the "don't print if it's None" enter? I doubt if there is a really good way to divide functionality. OF course, specific IDEs may provide their own hooks.
You're right! But a default is easy enough to add.
I agree. It was more to spur discussion -- with the advantage that there is already a way to include Python sessions.
I'd put it in sys instead of __builtin__ though.
Hmmm.. that's a Guido Issue(TM). Guido? -- Moshe Zadka moshez@math.huji.ac.il http://www.oreilly.com/news/prescod_0300.html http://www.linux.org.il -- we put the penguin in .com
Continuing the recent debate about what is appropriate to the interactive prompt printing, and the wide agreement that whatever we decide, users might think otherwise, I've written up a patch to have the user control via a function in __builtin__ the way things are printed at the prompt. This is not patches@python level stuff for two reasons:
- I'm not sure what to call this function. Currently, I call it
__print_expr__, but I'm not sure it's a good name
- I haven't yet supplied a default in __builtin__, so the user *must*
override this. This is unacceptable, of course.
I'd just like people to tell me if they think this is worth while, and if there is anything I missed.
Thanks for bringing this up again. I think it should be called sys.displayhook. The default could be something like
import __builtin__ def displayhook(obj): if obj is None: return __builtin__._ = obj sys.stdout.write("%s\n" % repr(obj))
to be nearly 100% compatible with current practice; or use str(obj) to do what most people would probably prefer.
(Note that you couldn't do "%s\n" % obj because obj might be a tuple.)
--Guido van Rossum (home page: http://www.python.org/~guido/)
Thanks for bringing this up again. I think it should be called sys.displayhook.
That should be the easy part -- I'll do it as soon as I'm home.
The default could be something like
import __builtin__
import sys # Sorry, I couldn't resist
def displayhook(obj): if obj is None: return __builtin__._ = obj sys.stdout.write("%s\n" % repr(obj))
This brings up a painful point -- the reason I haven't wrote the default is because it was way much easier to write it in Python. Of course, I shouldn't be preaching Python-is-easier-to-write-then-C here, but it pains me Python cannot be written with more Python and less C.
A while ago we started talking about the mini-interpreter idea, which would then freeze Python code into itself, and then it sort of died out. What have become of it?
-- Moshe Zadka moshez@math.huji.ac.il http://www.oreilly.com/news/prescod_0300.html http://www.linux.org.il -- we put the penguin in .com
import __builtin__
import sys # Sorry, I couldn't resist
def displayhook(obj): if obj is None: return __builtin__._ = obj sys.stdout.write("%s\n" % repr(obj))
This brings up a painful point -- the reason I haven't wrote the default is because it was way much easier to write it in Python. Of course, I shouldn't be preaching Python-is-easier-to-write-then-C here, but it pains me Python cannot be written with more Python and less C.
But the C code on how to do it was present in the code you deleted from ceval.c!
A while ago we started talking about the mini-interpreter idea, which would then freeze Python code into itself, and then it sort of died out. What have become of it?
Nobody sent me a patch :-(
--Guido van Rossum (home page: http://www.python.org/~guido/)
On Tue, 2 May 2000, Moshe Zadka wrote:
Thanks for bringing this up again. I think it should be called sys.displayhook.
I apologize profusely for dropping the ball on this. I was going to do it; i have been having a tough time lately figuring out a Big Life Decision. (Hate those BLDs.)
I was partway through hacking the patch and didn't get back to it, but i wanted to at least air the plan i had in mind. I hope you'll allow me this indulgence.
I was planning to submit a patch that adds the built-in routines
sys.display sys.displaytb
sys.__display__ sys.__displaytb__
sys.display(obj) would be implemented as 'print repr(obj)' and sys.displaytb(tb, exc) would call the same built-in traceback printer we all know and love.
I assumed that sys.__stdin__ was added to make it easier to restore sys.stdin to its original value. In the same vein, sys.__display__ and sys.__displaytb__ would be saved references to the original sys.display and sys.displaytb.
I hate to contradict Guido, but i'll gently suggest why i like "display" better than "displayhook": "display" is a verb, and i prefer function names to be verbs rather than nouns describing what the functions are (e.g. "read" rather than "reader", etc.)
-- ?!ng
I was planning to submit a patch that adds the built-in routines
sys.display sys.displaytb sys.__display__ sys.__displaytb__sys.display(obj) would be implemented as 'print repr(obj)' and sys.displaytb(tb, exc) would call the same built-in traceback printer we all know and love.
Sure. Though I would recommend to separate the patch in two parts, because their implementation is totally unrelated.
I assumed that sys.__stdin__ was added to make it easier to restore sys.stdin to its original value. In the same vein, sys.__display__ and sys.__displaytb__ would be saved references to the original sys.display and sys.displaytb.
Good idea.
I hate to contradict Guido, but i'll gently suggest why i like "display" better than "displayhook": "display" is a verb, and i prefer function names to be verbs rather than nouns describing what the functions are (e.g. "read" rather than "reader", etc.)
Good idea. But I hate the "displaytb" name (when I read your message I had no idea what the "tb" stood for until you explained it).
Hm, perhaps we could do showvalue and showtraceback? ("displaytraceback" is a bit long.)
--Guido van Rossum (home page: http://www.python.org/~guido/)
participants (4)
-
Fred L. Drake, Jr. -
Guido van Rossum -
Ka-Ping Yee -
Moshe Zadka