From 193747e9c3b5d09315e8848495e9e6f91437c733 Mon Sep 17 00:00:00 2001
From: Tom Augspurger <tom.w.augspurger@gmail.com>
Date: Fri, 9 Nov 2018 14:56:09 -0600
Subject: [PATCH] update docs, type

---
 pandas/core/arrays/base.py          | 16 ++++++++++++----
 pandas/core/arrays/integer.py       | 14 ++++++++------
 pandas/core/arrays/period.py        |  4 ++--
 pandas/tests/arrays/test_integer.py |  5 +++++
 4 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/pandas/core/arrays/base.py b/pandas/core/arrays/base.py
index d4a8da03913c3..be0b272f2816f 100644
--- a/pandas/core/arrays/base.py
+++ b/pandas/core/arrays/base.py
@@ -681,7 +681,7 @@ def __repr__(self):
                                dtype=self.dtype)
 
     def _formatter(self, formatter=None):
-        # type: (ExtensionArrayFormatter) -> Callable[Any]
+        # type: (Optional[ExtensionArrayFormatter]) -> Callable[[Any], str]
         """Formatting function for scalar values.
 
         This is used in the default '__repr__'. The formatting function
@@ -689,9 +689,17 @@ def _formatter(self, formatter=None):
 
         Parameters
         ----------
-        boxed: bool, default False
-            Whether the formatter is to be used by pandas inside a Series
-            or DataFrame repr.
+        formatter: GenericArrayFormatter, optional
+            The formatter this array is being rendered with. The formatter
+            may have a `.formatter` method already defined. By default, this
+            will be used if a `formatter` is passed, otherwise the formatter
+            is ``str``.
+
+        Returns
+        -------
+        Callable[[Any], str]
+            A callable that gets instances of the scalar type and
+            returns a string.
         """
         return getattr(formatter, 'formatter', None) or str
 
diff --git a/pandas/core/arrays/integer.py b/pandas/core/arrays/integer.py
index 984ef4c8c673c..98eb9df98328f 100644
--- a/pandas/core/arrays/integer.py
+++ b/pandas/core/arrays/integer.py
@@ -264,12 +264,14 @@ def _from_sequence(cls, scalars, dtype=None, copy=False):
     def _from_factorized(cls, values, original):
         return integer_array(values, dtype=original.dtype)
 
-    def _formatter(self, boxed=False):
-        def fmt(x):
-            if isna(x):
-                return 'NaN'
-            return str(x)
-        return fmt
+    def _formatter(self, formatter=None):
+        if formatter is None:
+            def fmt(x):
+                if isna(x):
+                    return 'NaN'
+                return str(x)
+            return fmt
+        return formatter.formatter
 
     def __getitem__(self, item):
         if is_integer(item):
diff --git a/pandas/core/arrays/period.py b/pandas/core/arrays/period.py
index 4f2848b3f5591..36a00db7625ce 100644
--- a/pandas/core/arrays/period.py
+++ b/pandas/core/arrays/period.py
@@ -330,8 +330,8 @@ def start_time(self):
     def end_time(self):
         return self.to_timestamp(how='end')
 
-    def _formatter(self, boxed=False):
-        if boxed:
+    def _formatter(self, formatter=None):
+        if formatter:
             return str
         return "'{}'".format
 
diff --git a/pandas/tests/arrays/test_integer.py b/pandas/tests/arrays/test_integer.py
index 6b99ede3436ce..94bf3dfd938a1 100644
--- a/pandas/tests/arrays/test_integer.py
+++ b/pandas/tests/arrays/test_integer.py
@@ -67,6 +67,11 @@ def test_repr_array(data):
     assert 'dtype: ' in result
 
 
+def test_na_repr(data):
+    result = repr(integer_array([1, None]))
+    assert 'NaN' in result
+
+
 def test_repr_array_long(data):
     # some arrays may be able to assert a ... in the repr
     with pd.option_context('display.max_seq_items', 1):