py/obj: Make mp_obj_get_complex_maybe call mp_obj_get_float_maybe first.

This commit simplifies mp_obj_get_complex_maybe() by first calling
mp_obj_get_float_maybe() to handle the cases corresponding to floats.
Only if that fails does it attempt to extra a full complex number.

This reduces code size and also means that mp_obj_get_complex_maybe() now
supports user-defined classes defining __float__; in particular this allows
user-defined classes to be used as arguments to cmath-module function.

Furthermore, complex_make_new() can now be simplified to directly call
mp_obj_get_complex(), instead of mp_obj_get_complex_maybe() followed by
mp_obj_get_float().  This also improves error messages from complex with
an invalid argument, it now raises "can't convert <type> to complex" rather
than "can't convert <type> to float".

Signed-off-by: Damien George <damien@micropython.org>

tests/float/cmath_dunder.py

@@ -0,0 +1,21 @@
+# test that cmath functions support user classes with __float__ and __complex__
+
+try:
+    import cmath
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+
+class TestFloat:
+    def __float__(self):
+        return 1.0
+
+
+class TestComplex:
+    def __complex__(self):
+        return 1j + 10
+
+
+for clas in TestFloat, TestComplex:
+    print("%.5g" % cmath.phase(clas()))

tests/float/complex_dunder.py

@@ -1,6 +1,11 @@
 # test __complex__ function support
 
 
+class TestFloat:
+    def __float__(self):
+        return 1.0
+
+
 class TestComplex:
     def __complex__(self):
         return 1j + 10
@@ -20,6 +25,7 @@ class Test:
     pass
 
 
+print(complex(TestFloat()))
 print(complex(TestComplex()))
 
 try:

tests/float/math_dunder.py

@@ -0,0 +1,15 @@
+# test that math functions support user classes with __float__
+
+try:
+    import math
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+
+class TestFloat:
+    def __float__(self):
+        return 1.0
+
+
+print("%.5g" % math.exp(TestFloat()))