From 71e8b3169b77149923afd39e70fb52c4277d7ebb Mon Sep 17 00:00:00 2001
From: Simon Hawkins <simonjayhawkins@gmail.com>
Date: Thu, 4 Apr 2019 00:02:54 +0100
Subject: [PATCH 1/2] to_html formatter not called for float values in a
 mixed-type column

---
 doc/source/whatsnew/v0.25.0.rst         |  1 +
 pandas/io/formats/format.py             | 17 +++++++++++------
 pandas/tests/io/formats/test_to_html.py | 10 ++++++++++
 3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/doc/source/whatsnew/v0.25.0.rst b/doc/source/whatsnew/v0.25.0.rst
index 1ef05ae5f9c6b..e01185b54f49d 100644
--- a/doc/source/whatsnew/v0.25.0.rst
+++ b/doc/source/whatsnew/v0.25.0.rst
@@ -344,6 +344,7 @@ I/O
 ^^^
 
 - Bug in :func:`DataFrame.to_html()` where values were truncated using display options instead of outputting the full content (:issue:`17004`)
+- Bug in :meth:`DataFrame.to_html` that would ignore ``formatters`` argument for float values in a column with ``dtype=object`` (:issue:`13021`)
 - Fixed bug in missing text when using :meth:`to_clipboard` if copying utf-16 characters in Python 3 on Windows (:issue:`25040`)
 - Bug in :func:`read_json` for ``orient='table'`` when it tries to infer dtypes by default, which is not applicable as dtypes are already defined in the JSON schema (:issue:`21345`)
 - Bug in :func:`read_json` for ``orient='table'`` and float index, as it infers index dtype by default, which is not applicable because index dtype is already defined in the JSON schema (:issue:`25433`)
diff --git a/pandas/io/formats/format.py b/pandas/io/formats/format.py
index b658c8a53dc8b..e2f01e03e3cef 100644
--- a/pandas/io/formats/format.py
+++ b/pandas/io/formats/format.py
@@ -980,6 +980,17 @@ def _format(x):
         if leading_space is None:
             leading_space = is_float_type.any()
 
+        if leading_space is False:
+            # False specifically, so that the default is
+            # to include a space if we get here.
+            tpl = '{v}'
+        else:
+            tpl = ' {v}'
+
+        # shortcut
+        if self.formatter is not None:
+            return [tpl.format(v=self.formatter(x)) for x in self.values]
+
         fmt_values = []
         for i, v in enumerate(vals):
             if not is_float_type[i] and leading_space:
@@ -987,12 +998,6 @@ def _format(x):
             elif is_float_type[i]:
                 fmt_values.append(float_format(v))
             else:
-                if leading_space is False:
-                    # False specifically, so that the default is
-                    # to include a space if we get here.
-                    tpl = '{v}'
-                else:
-                    tpl = ' {v}'
                 fmt_values.append(tpl.format(v=_format(v)))
 
         return fmt_values
diff --git a/pandas/tests/io/formats/test_to_html.py b/pandas/tests/io/formats/test_to_html.py
index d146e9c16e114..436dcff0aed60 100644
--- a/pandas/tests/io/formats/test_to_html.py
+++ b/pandas/tests/io/formats/test_to_html.py
@@ -633,3 +633,13 @@ def test_to_html_invalid_classes_type(classes):
 
     with pytest.raises(TypeError, match=msg):
         df.to_html(classes=classes)
+
+
+def test_to_html_formatters_object_type():
+    # GH 13021
+    def f(x):
+        return x if type(x) is str else '${:,.0f}'.format(x)
+
+    df = pd.DataFrame([['a'], [0], [10.4], [3]], columns=['x'])
+    result = df.to_html(formatters=dict(x=f))
+    assert '$10' in result

From 2a2bb57a9ee71c6686838df2ed47733865b015b0 Mon Sep 17 00:00:00 2001
From: Simon Hawkins <simonjayhawkins@gmail.com>
Date: Thu, 4 Apr 2019 20:30:28 +0100
Subject: [PATCH 2/2] changes to test as requested

---
 .../data/html/gh13021_expected_output.html    | 26 +++++++++++++++++++
 pandas/tests/io/formats/test_to_html.py       |  7 ++---
 2 files changed, 30 insertions(+), 3 deletions(-)
 create mode 100644 pandas/tests/io/formats/data/html/gh13021_expected_output.html

diff --git a/pandas/tests/io/formats/data/html/gh13021_expected_output.html b/pandas/tests/io/formats/data/html/gh13021_expected_output.html
new file mode 100644
index 0000000000000..55d864d8a0d3d
--- /dev/null
+++ b/pandas/tests/io/formats/data/html/gh13021_expected_output.html
@@ -0,0 +1,26 @@
+<table border="1" class="dataframe">
+  <thead>
+    <tr style="text-align: right;">
+      <th></th>
+      <th>x</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <th>0</th>
+      <td>a</td>
+    </tr>
+    <tr>
+      <th>1</th>
+      <td>$0</td>
+    </tr>
+    <tr>
+      <th>2</th>
+      <td>$10</td>
+    </tr>
+    <tr>
+      <th>3</th>
+      <td>$3</td>
+    </tr>
+  </tbody>
+</table>
diff --git a/pandas/tests/io/formats/test_to_html.py b/pandas/tests/io/formats/test_to_html.py
index 436dcff0aed60..29da4de36bf66 100644
--- a/pandas/tests/io/formats/test_to_html.py
+++ b/pandas/tests/io/formats/test_to_html.py
@@ -635,11 +635,12 @@ def test_to_html_invalid_classes_type(classes):
         df.to_html(classes=classes)
 
 
-def test_to_html_formatters_object_type():
+def test_to_html_formatters_object_type(datapath):
     # GH 13021
     def f(x):
-        return x if type(x) is str else '${:,.0f}'.format(x)
+        return x if isinstance(x, str) else '${:,.0f}'.format(x)
 
     df = pd.DataFrame([['a'], [0], [10.4], [3]], columns=['x'])
     result = df.to_html(formatters=dict(x=f))
-    assert '$10' in result
+    expected = expected_html(datapath, 'gh13021_expected_output')
+    assert result == expected