Improve docstrings for isnan, isinf and isfinite.
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index 152788f..69e1423 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -1828,7 +1828,7 @@
PyDoc_STRVAR(math_isfinite_doc,
"isfinite(x) -> bool\n\n\
-Check if float x is finite (not an infinity or NaN).");
+Return True if x is neither an infinity nor a NaN, and False otherwise.");
static PyObject *
math_isnan(PyObject *self, PyObject *arg)
@@ -1841,7 +1841,7 @@
PyDoc_STRVAR(math_isnan_doc,
"isnan(x) -> bool\n\n\
-Check if float x is not a number (NaN).");
+Return True if x is a NaN (not a number), and False otherwise.");
static PyObject *
math_isinf(PyObject *self, PyObject *arg)
@@ -1854,7 +1854,7 @@
PyDoc_STRVAR(math_isinf_doc,
"isinf(x) -> bool\n\n\
-Check if float x is infinite (positive or negative).");
+Return True if x is a positive or negative infinity, and False otherwise.");
static PyMethodDef math_methods[] = {
{"acos", math_acos, METH_O, math_acos_doc},