Issue #9416: Fix some issues with complex formatting where the

output with no type specifier failed to match the str output:

  - format(complex(-0.0, 2.0), '-') omitted the real part from the output,
  - format(complex(0.0, 2.0), '-') included a sign and parentheses.

Lib/test/test_complex.py

@@ -506,6 +506,16 @@ class ComplexTest(unittest.TestCase):
         self.assertEqual(format(z, '-'), str(z))
         self.assertEqual(format(z, '<'), str(z))
         self.assertEqual(format(z, '10'), str(z))
+        z = complex(0.0, 3.0)
+        self.assertEqual(format(z, ''), str(z))
+        self.assertEqual(format(z, '-'), str(z))
+        self.assertEqual(format(z, '<'), str(z))
+        self.assertEqual(format(z, '2'), str(z))
+        z = complex(-0.0, 2.0)
+        self.assertEqual(format(z, ''), str(z))
+        self.assertEqual(format(z, '-'), str(z))
+        self.assertEqual(format(z, '<'), str(z))
+        self.assertEqual(format(z, '3'), str(z))
 
         self.assertEqual(format(1+3j, 'g'), '1+3j')
         self.assertEqual(format(3j, 'g'), '0+3j')

Misc/NEWS

@@ -12,6 +12,12 @@ What's New in Python 3.2 Alpha 2?
 Core and Builtins
 -----------------
 
+- Issue #9416: Fix some issues with complex formatting where the
+  output with no type specifier failed to match the str output:
+
+    - format(complex(-0.0, 2.0), '-') omitted the real part from the output,
+    - format(complex(0.0, 2.0), '-') included a sign and parentheses.
+
 Library
 -------
 

Objects/stringlib/formatter.h

@@ -1136,9 +1136,10 @@ format_complex_internal(PyObject *value,
         /* Omitted type specifier. Should be like str(self). */
         type = 'g';
         default_precision = PyFloat_STR_PRECISION;
-        add_parens = 1;
-        if (re == 0.0)
+        if (re == 0.0 && copysign(1.0, re) == 1.0)
             skip_re = 1;
+        else
+            add_parens = 1;
     }
 
     if (type == 'n')
@@ -1223,8 +1224,11 @@ format_complex_internal(PyObject *value,
                                     n_re_digits, n_re_remainder,
                                     re_has_decimal, &locale, &tmp_format);
 
-    /* Same formatting, but always include a sign. */
-    tmp_format.sign = '+';
+    /* Same formatting, but always include a sign, unless the real part is
+     * going to be omitted, in which case we use whatever sign convention was
+     * requested by the original format. */
+    if (!skip_re)
+        tmp_format.sign = '+';
     n_im_total = calc_number_widths(&im_spec, 0, im_sign_char, p_im,
                                     n_im_digits, n_im_remainder,
                                     im_has_decimal, &locale, &tmp_format);