change to IO and add comment

Author: AntonioAndraues

doc/source/whatsnew/v1.0.0.rst

@@ -354,6 +354,7 @@ I/O
 - Bug in :func:`read_hdf` closing stores that it didn't open when Exceptions are raised (:issue:`28699`)
 - Bug in :meth:`DataFrame.read_json` where using ``orient="index"`` would not maintain the order (:issue:`28557`)
 - Bug in :meth:`DataFrame.to_html` where the length of the ``formatters`` argument was not verified (:issue:`28469`)
+- Bug in :meth:`pandas.io.formats.style.Styler` formatting for floating values not displaying decimals correctly (:issue:`13257`)
 
 Plotting
 ^^^^^^^^

pandas/tests/io/formats/test_style.py

@@ -1158,6 +1158,7 @@ def test_display_format_raises(self):
             df.style.format(True)
 
     def test_display_set_precision(self):
+        # Issue #13257
         df = pd.DataFrame(data=[[1.0, 2.0090], [3.2121, 4.566]], columns=["a", "b"])
         s = Styler(df)
 
@@ -1189,22 +1190,18 @@ def test_display_subset(self):
             {"a": "{:0.1f}", "b": "{0:.2%}"}, subset=pd.IndexSlice[0, :]
         )._translate()
         expected = "0.1"
-        assert ctx["body"][0][1]["display_value"] == expected
-        assert ctx["body"][1][1]["display_value"] == "1.1234"
-        assert ctx["body"][0][2]["display_value"] == "12.34%"
-
-        raw_11 = "1.1234"
-        ctx = df.style.format("{:0.1f}", subset=pd.IndexSlice[0, :])._translate()
+        raw_11 = "1.123400"
         assert ctx["body"][0][1]["display_value"] == expected
         assert ctx["body"][1][1]["display_value"] == raw_11
+        assert ctx["body"][0][2]["display_value"] == "12.34%"
 
         ctx = df.style.format("{:0.1f}", subset=pd.IndexSlice[0, :])._translate()
         assert ctx["body"][0][1]["display_value"] == expected
         assert ctx["body"][1][1]["display_value"] == raw_11
 
         ctx = df.style.format("{:0.1f}", subset=pd.IndexSlice["a"])._translate()
         assert ctx["body"][0][1]["display_value"] == expected
-        assert ctx["body"][0][2]["display_value"] == "0.1234"
+        assert ctx["body"][0][2]["display_value"] == "0.123400"
 
         ctx = df.style.format("{:0.1f}", subset=pd.IndexSlice[0, "a"])._translate()
         assert ctx["body"][0][1]["display_value"] == expected
@@ -1215,8 +1212,8 @@ def test_display_subset(self):
         )._translate()
         assert ctx["body"][0][1]["display_value"] == expected
         assert ctx["body"][1][1]["display_value"] == "1.1"
-        assert ctx["body"][0][2]["display_value"] == "0.1234"
-        assert ctx["body"][1][2]["display_value"] == "1.1234"
+        assert ctx["body"][0][2]["display_value"] == "0.123400"
+        assert ctx["body"][1][2]["display_value"] == raw_11
 
     def test_display_dict(self):
         df = pd.DataFrame([[0.1234, 0.1234], [1.1234, 1.1234]], columns=["a", "b"])