implementation for Decimal

python · mdickinson · Apr 11, 2022 · Dec 7, 2021 · Dec 11, 2021 · Dec 13, 2021
commit 3f4085d88b0b8e073ea83b41fc050aa028701f9f
diff --git a/Lib/_pydecimal.py b/Lib/_pydecimal.py
@@ -3795,6 +3795,10 @@ def __format__(self, specifier, context=None, _localeconv=None):
         # represented in fixed point; rescale them to 0e0.
         if not self and self._exp > 0 and spec['type'] in 'fF%':
             self = self._rescale(0, rounding)
+        if not self and spec['coerce_neg_0'] and self._sign:
+            adjusted_sign = 0
+        else:
+            adjusted_sign = self._sign
 
         # figure out placement of the decimal point
         leftdigits = self._exp + len(self._int)
@@ -3825,7 +3829,7 @@ def __format__(self, specifier, context=None, _localeconv=None):
 
         # done with the decimal-specific stuff;  hand over the rest
         # of the formatting to the _format_number function
-        return _format_number(self._sign, intpart, fracpart, exp, spec)
+        return _format_number(adjusted_sign, intpart, fracpart, exp, spec)
 
 def _dec_from_triple(sign, coefficient, exponent, special=False):
     """Create a decimal instance directly, without any validation,
@@ -6143,14 +6147,15 @@ def _convert_for_comparison(self, other, equality_op=False):
 #
 # A format specifier for Decimal looks like:
 #
-#   [[fill]align][sign][#][0][minimumwidth][,][.precision][type]
+#   [[fill]align][sign][z][#][0][minimumwidth][,][.precision][type]
 
 _parse_format_specifier_regex = re.compile(r"""\A
 (?:
    (?P<fill>.)?
    (?P<align>[<>=^])
 )?
 (?P<sign>[-+ ])?
+(?P<coerce_neg_0>z)?
 (?P<alt>\#)?
 (?P<zeropad>0)?
 (?P<minimumwidth>(?!0)\d+)?

diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
@@ -1071,6 +1071,39 @@ def test_formatting(self):
             (',e', '123456', '1.23456e+5'),
             (',E', '123456', '1.23456E+5'),
 
+            # negative zero: default behavior
+            ('.1f', '-0', '-0.0'),
+            ('.1f', '-.0', '-0.0'),
+            ('.1f', '-.01', '-0.0'),
+
+            # negative zero: z option
+            ('z.1f', '0.', '0.0'),
+            ('z6.1f', '0.', '   0.0'),
+            ('z6.1f', '-1.', '  -1.0'),
+            ('z.1f', '-0.', '0.0'),
+            ('z.1f', '.01', '0.0'),
+            ('z.1f', '-.01', '0.0'),
+            ('z.2f', '0.', '0.00'),
+            ('z.2f', '-0.', '0.00'),
+            ('z.2f', '.001', '0.00'),
+            ('z.2f', '-.001', '0.00'),
+
+            ('z.1e', '0.', '0.0e+1'),
+            ('z.1e', '-0.', '0.0e+1'),
+            ('z.1E', '0.', '0.0E+1'),
+            ('z.1E', '-0.', '0.0E+1'),
+
+            ('z.1f', '-00000.000001', '0.0'),
+            ('z.1f', '-00000.', '0.0'),
+            ('z.1f', '-.0000000000', '0.0'),
+
+            ('z.2f', '-00000.000001', '0.00'),
+            ('z.2f', '-00000.', '0.00'),
+            ('z.2f', '-.0000000000', '0.00'),
+
+            ('z.1f', '.09', '0.1'),
+            ('z.1f', '-.09', '-0.1'),
+
             # issue 6850
             ('a=-7.0', '0.12345', 'aaaa0.1'),
 

diff --git a/Lib/test/test_format.py b/Lib/test/test_format.py
@@ -1,4 +1,3 @@
-from decimal import Decimal
 from test.support import verbose, TestFailed
 import locale
 import sys
@@ -552,7 +551,6 @@ def test_negative_zero(self):
         self.assertEqual(f"{-0.:.1f}", "-0.0")
         self.assertEqual(f"{-.01:.1f}", "-0.0")
         self.assertEqual(f"{-0:.1f}", "0.0")  # integers do not distinguish -0
-        self.assertEqual(f"{Decimal('-0'):.1f}", "-0.0")
 
         ## z sign option
         self.assertEqual(f"{0.:z.1f}", "0.0")

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
@@ -3221,9 +3221,11 @@ dec_format(PyObject *dec, PyObject *args)
     PyObject *context;
     mpd_spec_t spec;
     char *fmt;
+    char *fmt_copy = NULL;
     char *decstring = NULL;
     uint32_t status = 0;
     int replace_fillchar = 0;
+    int coerce_neg_0 = 0;
     Py_ssize_t size;
 
 
@@ -3241,11 +3243,24 @@ dec_format(PyObject *dec, PyObject *args)
             /* NUL fill character: must be replaced with a valid UTF-8 char
                before calling mpd_parse_fmt_str(). */
             replace_fillchar = 1;
-            fmt = dec_strdup(fmt, size);
-            if (fmt == NULL) {
+            fmt = fmt_copy = dec_strdup(fmt, size);
+            if (fmt_copy == NULL) {
                 return NULL;
             }
-            fmt[0] = '_';
+            fmt_copy[0] = '_';
+        }
+        char *z_start = strchr(fmt, 'z');
+        if (z_start != NULL) {
+            coerce_neg_0 = 1;
+            size_t z_index = z_start - fmt;
+            if (fmt_copy == NULL) {
+                fmt = fmt_copy = dec_strdup(fmt, size);
+                if (fmt_copy == NULL) {
+                    return NULL;
+                }
+            }
+            memmove(fmt_copy + z_index, fmt_copy + z_index + 1, size - z_index);
+            size -= 1;
         }
     }
     else {
@@ -3311,6 +3326,19 @@ dec_format(PyObject *dec, PyObject *args)
         }
     }
 
+    if (coerce_neg_0 && mpd_isnegative(MPD(dec)) && !mpd_isspecial(MPD(dec))) {
+        /* round into a temporary and clear sign if result is zero */
+        mpd_uint_t dt[MPD_MINALLOC_MAX];
+        mpd_t tmp = {MPD_STATIC|MPD_STATIC_DATA,0,0,0,MPD_MINALLOC_MAX,dt};
+        mpd_qrescale(&tmp, MPD(dec), -spec.prec, CTX(context), &status);
+        if (status & MPD_Errors) {
+            PyErr_SetString(PyExc_ValueError, "unexpected error when rounding");
+            goto finish;
+        }
+        if (mpd_iszero(&tmp)) {
+            mpd_set_positive(MPD(dec));
+        }
+    }
 
     decstring = mpd_qformat_spec(MPD(dec), &spec, CTX(context), &status);
     if (decstring == NULL) {
@@ -3335,7 +3363,7 @@ dec_format(PyObject *dec, PyObject *args)
     Py_XDECREF(grouping);
     Py_XDECREF(sep);
     Py_XDECREF(dot);
-    if (replace_fillchar) PyMem_Free(fmt);
+    if (fmt_copy) PyMem_Free(fmt_copy);
     if (decstring) mpd_free(decstring);
     return result;
 }