BUG: set_precision format fixed (#13257)

Co-Authored-By: Tom Augspurger <TomAugspurger@users.noreply.github.com>

Author: AntonioAndraues

doc/source/whatsnew/v1.0.0.rst

@@ -201,7 +201,7 @@ ExtensionArray
 Other
 ^^^^^
 - Trying to set the ``display.precision``, ``display.max_rows`` or ``display.max_columns`` using :meth:`set_option` to anything but a ``None`` or a positive int will raise a ``ValueError`` (:issue:`23348`)
-
+- Bug in :meth:`pandas.io.formats.style.Styler` formatting for floating values not displaying decimals correctly (:issue:`13257`)
 
 .. _whatsnew_1000.contributors:
 

pandas/io/formats/style.py

@@ -151,7 +151,8 @@ def __init__(
 
         def default_display_func(x):
             if is_float(x):
-                return "{:>.{precision}g}".format(x, precision=self.precision)
+                display_format = "{0:.{precision}f}".format(x, precision=self.precision)
+                return display_format.rstrip("0").rstrip(".")
             else:
                 return x
 

pandas/tests/io/formats/test_style.py

@@ -1157,6 +1157,32 @@ def test_display_format_raises(self):
         with pytest.raises(TypeError):
             df.style.format(True)
 
+    def test_display_set_precision(self):
+        df = pd.DataFrame(data=[[1.0, 2.0090], [3.2121, 4.566]], columns=["a", "b"])
+        s = Styler(df)
+
+        ctx = s.set_precision(1)._translate()
+
+        assert s.precision == 1
+        assert ctx["body"][0][1]["display_value"] == "1"
+        assert ctx["body"][0][2]["display_value"] == "2"
+        assert ctx["body"][1][1]["display_value"] == "3.2"
+        assert ctx["body"][1][2]["display_value"] == "4.6"
+
+        ctx = s.set_precision(2)._translate()
+        assert s.precision == 2
+        assert ctx["body"][0][1]["display_value"] == "1"
+        assert ctx["body"][0][2]["display_value"] == "2.01"
+        assert ctx["body"][1][1]["display_value"] == "3.21"
+        assert ctx["body"][1][2]["display_value"] == "4.57"
+
+        ctx = s.set_precision(3)._translate()
+        assert s.precision == 3
+        assert ctx["body"][0][1]["display_value"] == "1"
+        assert ctx["body"][0][2]["display_value"] == "2.009"
+        assert ctx["body"][1][1]["display_value"] == "3.212"
+        assert ctx["body"][1][2]["display_value"] == "4.566"
+
     def test_display_subset(self):
         df = pd.DataFrame([[0.1234, 0.1234], [1.1234, 1.1234]], columns=["a", "b"])
         ctx = df.style.format(