Use context's rounding mode per default in the format()

CHANGES

@@ -33,8 +33,8 @@ Features:
 * Implement mpf.__format__(), see #819, #831, #850, #859, #857, #862, #881,
   #944 and #966 (Javier Garcia, Sergey B Kirpichev)
 * Support conversion from scalar ndarray's, see #821 (Sergey B Kirpichev)
-* Support rounding modes in mpf.__format__, see #823, #831 and #834 (Javier
-  Garcia, Sergey B Kirpichev)
+* Support rounding modes in mpf.__format__, see #823, #831, #834
+  and #969 (Javier Garcia, Sergey B Kirpichev)
 * Support '%' presentation type for mpf, see #847 (Sergey B Kirpichev)
 * Support gmpy2-like rounding modes in to_str(), see #830 (Javier Garcia)
 * Implement 'a'/'A' formating types for mpf.__format__, see #841 and #870

mpmath/ctx_mp_python.py

@@ -396,6 +396,8 @@ class _mpf(mpnumeric):
             * ``'Z'``: rounding towards zero
             * ``'N'``: rounding to nearest (default)
 
+        If it's not specified, the context's rounding mode is used.
+
         The rounding option must be set right before the presentation type:
 
             >>> x = mp.mpf('-1.2345678')
@@ -428,9 +430,9 @@ class _mpf(mpnumeric):
 
         """
 
-        _, _, (prec, _) = s._ctxdata
+        _, _, (prec, rounding) = s._ctxdata
         ctx = s.context
-        return format_mpf(s._mpf_, format_spec, prec, ctx._pretty_repr_dps)
+        return format_mpf(s._mpf_, format_spec, prec, rounding, ctx._pretty_repr_dps)
 
     def sqrt(s):
         return s.context.sqrt(s)
@@ -701,9 +703,9 @@ class _mpc(mpnumeric):
 
         """
 
-        _, _, (prec, _) = s._ctxdata
+        _, _, (prec, rounding) = s._ctxdata
         ctx = s.context
-        return format_mpc(s._mpc_, format_spec, prec, ctx._pretty_repr_dps)
+        return format_mpc(s._mpc_, format_spec, prec, rounding, ctx._pretty_repr_dps)
 
 
 complex_types = (complex, _mpc)

mpmath/libmp/libmpf.py

@@ -1452,7 +1452,6 @@ def read_format_spec(format_spec):
         'frac_separators': '',
         'width': -1,
         'precision': -1,
-        'rounding': round_nearest,
         'type': ''
         }
 
@@ -1595,7 +1594,7 @@ def fill_sep(digits, sep, prev, nmod, sep_range):
                            for pos in range(nmod, len(digits), sep_range))
 
 
-def format_digits(num, format_dict, prec, _pretty_repr_dps):
+def format_digits(num, format_dict, prec, rnd, _pretty_repr_dps):
     capitalize = False
     if format_dict['type'] in list('AFGE'):
         capitalize = True
@@ -1618,7 +1617,7 @@ def format_digits(num, format_dict, prec, _pretty_repr_dps):
     strip_last_zero = False
     strip_zeros = False
 
-    rnd = format_dict['rounding']
+    rnd = format_dict.get('rounding', rnd)
 
     if not fmt_type or fmt_type == 'g':
         if not format_dict['alternate']:
@@ -1729,9 +1728,9 @@ def format_digits(num, format_dict, prec, _pretty_repr_dps):
     return sign, int_part + digits
 
 
-def format_mpf(num, format_spec, prec, _pretty_repr_dps):
+def format_mpf(num, format_spec, prec, rnd, _pretty_repr_dps):
     format_dict = read_format_spec(format_spec)
-    sign, digits = format_digits(num, format_dict, prec, _pretty_repr_dps)
+    sign, digits = format_digits(num, format_dict, prec, rnd, _pretty_repr_dps)
     nchars = len(digits) + len(sign)
     lpad, rpad = calc_padding(
             nchars, format_dict['width'], format_dict['align'])
@@ -1744,7 +1743,7 @@ def format_mpf(num, format_spec, prec, _pretty_repr_dps):
             + rpad*format_dict['fill_char']
 
 
-def format_mpc(num, format_spec, prec, _pretty_repr_dps):
+def format_mpc(num, format_spec, prec, rnd, _pretty_repr_dps):
     format_dict = read_format_spec(format_spec)
 
     if format_dict['fill_char'] == '0':
@@ -1760,10 +1759,10 @@ def format_mpc(num, format_spec, prec, _pretty_repr_dps):
     fmt_type = format_dict['type'].lower()
     if not fmt_type:
         format_dict['type'] = 'g'
-    sign_re, digits_re = format_digits(num[0], format_dict, prec, _pretty_repr_dps)
+    sign_re, digits_re = format_digits(num[0], format_dict, prec, rnd, _pretty_repr_dps)
     fmt_sign = format_dict['sign']
     format_dict['sign'] = '+'
-    sign_im, digits_im = format_digits(num[1], format_dict, prec, _pretty_repr_dps)
+    sign_im, digits_im = format_digits(num[1], format_dict, prec, rnd, _pretty_repr_dps)
     digits_im += 'j'
 
     if not fmt_type:

mpmath/tests/test_format.py

@@ -806,6 +806,16 @@ def test_mpf_fmt():
             assert f"{mp.mpf('-0.1'):=.4Df}" == "-0.1000"
 
 
+def test_default_rounding():
+    x = mp.mpf(mp.pi)
+
+    assert f"{x:.3f}" == '3.142'
+    mp.rounding = 'd'
+    assert f"{x:.3f}" == '3.141'
+    mp.rounding = 'u'
+    assert f"{x:.3f}" == '3.142'
+
+
 def test_issue_858():
     for n in range(2, 15):
         str_num = '0.' + (n)*'9'