BUG: add check for infinity in __call__ of EngFormatter

EngFormatter throws an exception if passed 'inf' as below.    This
patch checks for infinity and just returns 'inf' in that case.

xref #11981

Author: Johnny Gill <[email protected]>

Closes #14214 from swfiua/master and squashes the following commits:

f2348e7 [Johnny Gill] test EngFormatter with np.inf
83f4091 [Johnny Gill] add check for infinity in __call__ of EngFormatter

Author: swfiua

doc/source/whatsnew/v0.19.0.txt

@@ -1507,7 +1507,7 @@ Bug Fixes
 - Bug in ``Series`` and ``Index`` comparison may output incorrect result if it contains ``NaT`` with ``object`` dtype (:issue:`13592`)
 - Bug in ``Period`` addition raises ``TypeError`` if ``Period`` is on right hand side (:issue:`13069`)
 - Bug in ``Peirod`` and ``Series`` or ``Index`` comparison raises ``TypeError`` (:issue:`13200`)
-- Bug in ``pd.set_eng_float_format()`` that would prevent NaN's from formatting (:issue:`11981`)
+- Bug in ``pd.set_eng_float_format()`` that would prevent NaN and Inf from formatting (:issue:`11981`)
 - Bug in ``.unstack`` with ``Categorical`` dtype resets ``.ordered`` to ``True`` (:issue:`13249`)
 - Clean some compile time warnings in datetime parsing (:issue:`13607`)
 - Bug in ``factorize`` raises ``AmbiguousTimeError`` if data contains datetime near DST boundary (:issue:`13750`)

pandas/formats/format.py

@@ -2586,6 +2586,9 @@ def __call__(self, num):
         if decimal.Decimal.is_nan(dnum):
             return 'NaN'
 
+        if decimal.Decimal.is_infinite(dnum):
+            return 'inf'
+
         sign = 1
 
         if dnum < 0:  # pragma: no cover

pandas/tests/formats/test_format.py

@@ -4047,6 +4047,14 @@ def test_nan(self):
         self.assertTrue('NaN' in result)
         self.reset_display_options()
 
+    def test_inf(self):
+        # Issue #11981
+
+        formatter = fmt.EngFormatter(accuracy=1, use_eng_prefix=True)
+        result = formatter(np.inf)
+        self.assertEqual(result, u('inf'))
+
+
 def _three_digit_exp():
     return '%.4g' % 1.7e8 == '1.7e+008'