New submission from Mark Dickinson <[email protected]>:
Our abstract objects layer in the C-API includes PyNumber_Float [1], which is
equivalent to a Python-level `float` call, including the behaviour of accepting
strings. I'm not convinced that it's a particularly useful function: I suspect
that it's more common to need to either convert a string to a float, or to
convert a float-y object (i.e., something whose type implements __float__) to a
float, but not both at once. The second need is precisely the one that most of
the math module has: accept anything that implements __float__, but don't
accept strings.
Yesterday I found myself writing the following code for a 3rd-party extension
module:
static PyObject *
_validate_float(PyObject *value) {
double value_as_double;
/* Fast path: avoid creating a new object if it's not necessary. */
if (PyFloat_CheckExact(value)) {
Py_INCREF(value);
return value;
}
value_as_double = PyFloat_AsDouble(value);
if (value_as_double == -1.0 && PyErr_Occurred()) {
return NULL;
}
return PyFloat_FromDouble(value_as_double);
}
Would it be worth adding a new C-API level function that does essentially the
above? The semantics of such a function seem clear cut. The major problem would
be figuring out what to call it, since to me PyNumber_Float is the one obvious
name for such behaviour, but it's already taken. :-)
Please note that I'm not suggesting removing / deprecating / changing the
existing PyNumber_Float. That would amount to gratuitous breakage.
[1] https://docs.python.org/3.6/c-api/number.html#c.PyNumber_Float
----------
components: Interpreter Core
messages: 311819
nosy: mark.dickinson
priority: normal
severity: normal
status: open
title: PyNumber_Float counterpart that doesn't accept strings
type: enhancement
versions: Python 3.8
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Python tracker <[email protected]>
<https://bugs.python.org/issue32794>
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