On 06/06/2017 11:22 AM, Skip Montanaro wrote:
> On Tue, Jun 6, 2017 at 12:27 PM, Chris Angelico <ros...@gmail.com> wrote:
>> Or perhaps showing the repr of the string would be clearer.
>
> This would definitely be better, I think, and require no special
> casing of the empty string. Still, I doubt this would ever be
> backported for fear of breaking code might be out there somewhere
> which relies on the current behavior. At best, it might be added to
> the next 3.x release (3.7?).
>
> Skip
>
Does it make sense to open a bug report? I'm always a bit intimidated by
contributing to python, but the following patch does seem to work
(against a new clone of the master branch):
----------------------
$ git diff
diff --git a/Python/pystrtod.c b/Python/pystrtod.c
index 64d0c52..b3d84e4 100644
--- a/Python/pystrtod.c
+++ b/Python/pystrtod.c
@@ -355,9 +355,15 @@ PyOS_string_to_double(const char *s,
"could not convert string to float: "
"%.200s", s);
else if (fail_pos == s)
- PyErr_Format(PyExc_ValueError,
- "could not convert string to float: "
- "%.200s", s);
+ if (*s == 0) {
+ PyErr_Format(PyExc_ValueError,
+ "could not convert string to float: ''");
+ }
+ else {
+ PyErr_Format(PyExc_ValueError,
+ "could not convert string to float: "
+ "%.200s", s);
+ }
else if (errno == ERANGE && fabs(x) >= 1.0 && overflow_exception)
PyErr_Format(overflow_exception,
"value too large to convert to float: "
----------------------
My changes feel a bit hacky. I wanted to just drop a straight repr() in,
but I didn't want to change the code too much since I assume the string
formatting is already there for a reason (e.g. "%.200s").
In any case, that patch seems to be working at first glance:
>>> float('')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: ''
>>> float('a')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: 'a'
>>> float('1')
1.0
Cheers,
Thomas
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