Issue #3382. float 'F' formatting no longer maps to 'f'. This only affects nan and inf.

Doc/library/string.rst

@@ -415,7 +415,8 @@ The available presentation types for floating point and decimal values are:
    | ``'f'`` | Fixed point. Displays the number as a fixed-point        |
    |         | number.                                                  |
    +---------+----------------------------------------------------------+
-   | ``'F'`` | Fixed point. Same as ``'f'``.                            |
+   | ``'F'`` | Fixed point. Same as ``'f'``, but converts ``nan`` to    |
+   |         | ``NAN`` and ``inf`` to ``INF``.                          |
    +---------+----------------------------------------------------------+
    | ``'g'`` | General format. This prints the number as a fixed-point  |
    |         | number, unless the number is too large, in which case    |

Lib/test/test_complex.py

@@ -507,6 +507,24 @@ class ComplexTest(unittest.TestCase):
         # make sure everything works in ''.format()
         self.assertEqual('*{0:.3f}*'.format(3.14159+2.71828j), '*3.142+2.718j*')
 
+        # issue 3382
+        self.assertEqual(format(complex(NAN, NAN), 'f'), 'nan+nanj')
+        self.assertEqual(format(complex(1, NAN), 'f'), '1.000000+nanj')
+        self.assertEqual(format(complex(NAN, 1), 'f'), 'nan+1.000000j')
+        self.assertEqual(format(complex(NAN, -1), 'f'), 'nan-1.000000j')
+        self.assertEqual(format(complex(NAN, NAN), 'F'), 'NAN+NANj')
+        self.assertEqual(format(complex(1, NAN), 'F'), '1.000000+NANj')
+        self.assertEqual(format(complex(NAN, 1), 'F'), 'NAN+1.000000j')
+        self.assertEqual(format(complex(NAN, -1), 'F'), 'NAN-1.000000j')
+        self.assertEqual(format(complex(INF, INF), 'f'), 'inf+infj')
+        self.assertEqual(format(complex(1, INF), 'f'), '1.000000+infj')
+        self.assertEqual(format(complex(INF, 1), 'f'), 'inf+1.000000j')
+        self.assertEqual(format(complex(INF, -1), 'f'), 'inf-1.000000j')
+        self.assertEqual(format(complex(INF, INF), 'F'), 'INF+INFj')
+        self.assertEqual(format(complex(1, INF), 'F'), '1.000000+INFj')
+        self.assertEqual(format(complex(INF, 1), 'F'), 'INF+1.000000j')
+        self.assertEqual(format(complex(INF, -1), 'F'), 'INF-1.000000j')
+
 def test_main():
     support.run_unittest(ComplexTest)
 

Lib/test/test_float.py

@@ -320,6 +320,12 @@ class FormatTestCase(unittest.TestCase):
                 self.assertRaises(ValueError, format, 1e-100, format_spec)
                 self.assertRaises(ValueError, format, -1e-100, format_spec)
 
+        # issue 3382
+        self.assertEqual(format(NAN, 'f'), 'nan')
+        self.assertEqual(format(NAN, 'F'), 'NAN')
+        self.assertEqual(format(INF, 'f'), 'inf')
+        self.assertEqual(format(INF, 'F'), 'INF')
+
     @unittest.skipUnless(float.__getformat__("double").startswith("IEEE"),
                          "test requires IEEE 754 doubles")
     def test_format_testfile(self):

Lib/test/test_unicode.py

@@ -779,6 +779,14 @@ class UnicodeTest(
                 return '\u1234'
         self.assertEqual('%s' % Wrapper(), '\u1234')
 
+        # issue 3382
+        NAN = float('nan')
+        INF = float('inf')
+        self.assertEqual('%f' % NAN, 'nan')
+        self.assertEqual('%F' % NAN, 'NAN')
+        self.assertEqual('%f' % INF, 'inf')
+        self.assertEqual('%F' % INF, 'INF')
+
     @support.run_with_locale('LC_ALL', 'de_DE', 'fr_FR')
     def test_format_float(self):
         # should not format with a comma, but always with C locale

Misc/NEWS

@@ -12,6 +12,10 @@ What's New in Python 3.1 beta 1?
 Core and Builtins
 -----------------
 
+- Issue #3382: float.__format__, complex.__format__, and %-formatting
+  no longer map 'F' to 'f'. Because of issue #5859 (below), this only
+  affects nan -> NAN and inf -> INF.
+
 - Issue #5799: ntpath (ie, os.path on Windows) fully supports UNC pathnames
   in all operations, including splitdrive, split, etc.  splitunc() now issues
   a PendingDeprecation warning.
@@ -45,7 +49,7 @@ Core and Builtins
   restrictions for float formatting: '%.67f' % 12.34 and '%.120e' %
   12.34 no longer raise an exception.
 
-- Issue #1588: Add complex.__format__. For example, 
+- Issue #1588: Add complex.__format__. For example,
   format(complex(1, 2./3), '.5') now produces a sensible result.
 
 - Issue #5864: Fix empty format code formatting for floats so that it

Objects/stringlib/formatter.h

@@ -920,10 +920,6 @@ format_float_internal(PyObject *value,
            format the result. We take care of that later. */
         type = 'g';
 
-    /* 'F' is the same as 'f', per the PEP */
-    if (type == 'F')
-        type = 'f';
-
     val = PyFloat_AsDouble(value);
     if (val == -1.0 && PyErr_Occurred())
         goto done;
@@ -939,8 +935,15 @@ format_float_internal(PyObject *value,
 
 #if PY_VERSION_HEX < 0x03010000
     /* 3.1 no longer converts large 'f' to 'g'. */
-    if ((type == 'f' || type == 'F') && fabs(val) >= 1e50)
-        type = 'g';
+    if (fabs(val) >= 1e50)
+        switch (type) {
+        case 'f':
+            type = 'g';
+            break;
+        case 'F':
+            type = 'G';
+            break;
+        }
 #endif
 
     /* Cast "type", because if we're in unicode we need to pass a
@@ -1114,10 +1117,6 @@ format_complex_internal(PyObject *value,
            format the result. We take care of that later. */
         type = 'g';
 
-    /* 'F' is the same as 'f', per the PEP */
-    if (type == 'F')
-        type = 'f';
-
     if (precision < 0)
         precision = default_precision;