Issue #5920: Changed format.__float__ and complex.__float__ to use a precision of 12 when using the empty presentation type. This more closely matches str()'s behavior and reduces surprises when adding alignment flags to an empty format string. Patch by Mark Dickinson.
diff --git a/Objects/floatobject.c b/Objects/floatobject.c
index 1071fae..1074f3d 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -294,11 +294,12 @@
 }
 
 static PyObject *
-float_str_or_repr(PyFloatObject *v, char format_code)
+float_str_or_repr(PyFloatObject *v, int precision, char format_code)
 {
     PyObject *result;
     char *buf = PyOS_double_to_string(PyFloat_AS_DOUBLE(v),
-                                      format_code, 0, Py_DTSF_ADD_DOT_0,
+                                      format_code, precision,
+                                      Py_DTSF_ADD_DOT_0,
                                       NULL);
     if (!buf)
         return PyErr_NoMemory();
@@ -310,13 +311,13 @@
 static PyObject *
 float_repr(PyFloatObject *v)
 {
-    return float_str_or_repr(v, 'r');
+    return float_str_or_repr(v, 0, 'r');
 }
 
 static PyObject *
 float_str(PyFloatObject *v)
 {
-    return float_str_or_repr(v, 's');
+    return float_str_or_repr(v, PyFloat_STR_PRECISION, 'g');
 }
 
 /* Comparison is pretty much a nightmare.  When comparing float to float,