bpo-36908: 'This module is always available' isn't helpful. (GH-13297)

Makes the documentation of math and cmath module
more helpful for the beginners.
(cherry picked from commit 6faad35)

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>

Doc/library/cmath.rst

@@ -6,13 +6,12 @@
 
 --------------
 
-This module is always available.  It provides access to mathematical functions
-for complex numbers.  The functions in this module accept integers,
-floating-point numbers or complex numbers as arguments. They will also accept
-any Python object that has either a :meth:`__complex__` or a :meth:`__float__`
-method: these methods are used to convert the object to a complex or
-floating-point number, respectively, and the function is then applied to the
-result of the conversion.
+This module provides access to mathematical functions for complex numbers.  The
+functions in this module accept integers, floating-point numbers or complex
+numbers as arguments. They will also accept any Python object that has either a
+:meth:`__complex__` or a :meth:`__float__` method: these methods are used to
+convert the object to a complex or floating-point number, respectively, and
+the function is then applied to the result of the conversion.
 
 .. note::
 

Doc/library/math.rst

@@ -10,8 +10,8 @@
 
 --------------
 
-This module is always available.  It provides access to the mathematical
-functions defined by the C standard.
+This module provides access to the mathematical functions defined by the C
+standard.
 
 These functions cannot be used with complex numbers; use the functions of the
 same name from the :mod:`cmath` module if you require support for complex

Modules/cmathmodule.c

@@ -1232,8 +1232,8 @@ cmath_isclose_impl(PyObject *module, Py_complex a, Py_complex b,
 }
 
 PyDoc_STRVAR(module_doc,
-"This module is always available. It provides access to mathematical\n"
-"functions for complex numbers.");
+"This module provides access to mathematical functions for complex\n"
+"numbers.");
 
 static PyMethodDef cmath_methods[] = {
     CMATH_ACOS_METHODDEF

Modules/mathmodule.c

@@ -2371,8 +2371,8 @@ static PyMethodDef math_methods[] = {
 
 
 PyDoc_STRVAR(module_doc,
-"This module is always available.  It provides access to the\n"
-"mathematical functions defined by the C standard.");
+"This module provides access to the mathematical functions\n"
+"defined by the C standard.");
 
 
 static struct PyModuleDef mathmodule = {