Feature Requests item #1634034, was opened at 2007-01-12 13:03
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Category: Parser/Compiler
Group: Python 2.6
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Oliver Gramberg (oliver_gramberg)
Assigned to: Nobody/Anonymous (nobody)
Summary: Show "expected" token on syntax error
Initial Comment:
I suggest that the parser, when reporting a syntax
error, should make use of its knowlegde of which token
type is expected at the position where the error
occurred. This results in more helpful error messages:
-----------------------------------------------------
>>> for a in (8,9)
File "<stdin>", line 1
for a in (8,9)
^
SyntaxError: invalid syntax - COLON expected
-----------------------------------------------------
>>> for a in (8,9: print a,
File "<stdin>", line 1
for a in (8,9: print a,
^
SyntaxError: invalid syntax: RPAR expected
-----------------------------------------------------
I tried the following patch (for pythonrun.c). It works
well in the shell both interactively and in scripts,
as well as in IDLE. But it's not complete:
- It doesn't always print useful messages (only for
fixed-size terminal token types, I assume.)
- There sure are cases where more than one token type
is allowed in a position. I believe I have seen that
this information is available too somewhere in the
parser, but it is not forwarded to the err_input
routine.
It's even nicer to show "')'" instead of "RPAR"...
-----------------------------------------------------
/* Set the error appropriate to the given input error code (see errcode.h) */
static void
err_input(perrdetail *err)
{
PyObject *v, *w, *errtype;
PyObject* u = NULL;
char *msg = NULL;
errtype = PyExc_SyntaxError;
switch (err->error) {
case E_SYNTAX:
errtype = PyExc_IndentationError;
if (err->expected == INDENT)
msg = "expected an indented block";
else if (err->token == INDENT)
msg = "unexpected indent";
else if (err->token == DEDENT)
msg = "unexpected unindent";
else {
char buf[50];
errtype = PyExc_SyntaxError;
if(err->expected != -1) {
snprintf(buf, 48, "invalid syntax - %.16s
expected\0",
_PyParser_TokenNames[err->expected]);
msg = buf;
} else {
msg = "invalid syntax";
}
}
break;
...
-----------------------------------------------------
I am willing to help work on this.
Regards
-Oliver
----------------------------------------------------------------------
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