Added deprecation warning and shim

Author: TomAugspurger

pandas/formats/__init__.py

@@ -0,0 +1,7 @@
+import warnings
+
+warnings.warn("Styler has been moved from pandas.formats.style.Styler"
+              " to pandas.io.formats.style.Styler. This shim will be"
+              " removed in pandas 0.21",
+              FutureWarning)
+from pandas.io.formats.style import Styler  # noqa

pandas/formats/style.py

@@ -747,3 +747,10 @@ def test_from_custom_template(tmpdir):
     assert result.template is not Styler.template
     styler = result(pd.DataFrame({"A": [1, 2]}))
     assert styler.render()
+
+
+def test_shim():
+    # https://github.com/pandas-dev/pandas/pull/16059
+    # Remove in 0.21
+    with pytest.warns(FutureWarning):
+        from pandas.formats.style import Styler as _styler  # noqa