BUG: Validate the justify parameter in to_html

Closes pandas-devgh-17527.

Author: gfyoung

doc/source/whatsnew/v0.21.0.txt

@@ -779,6 +779,7 @@ I/O
 - Bug in :func:`read_csv` where automatic delimiter detection caused a ``TypeError`` to be thrown when a bad line was encountered rather than the correct error message (:issue:`13374`)
 - Bug in ``DataFrame.to_html()`` with ``notebook=True`` where DataFrames with named indices or non-MultiIndex indices had undesired horizontal or vertical alignment for column or row labels, respectively (:issue:`16792`)
 - Bug in :func:`HDFStore.select` when reading a contiguous mixed-data table featuring VLArray (:issue:`17021`)
+- Bug in :func:`to_html` in which there was no validation of the ``justify`` parameter (:issue:`17527`)
 
 Plotting
 ^^^^^^^^

pandas/core/frame.py

@@ -1685,6 +1685,11 @@ def to_html(self, buf=None, columns=None, col_space=None, header=True,
             .. versionadded:: 0.19.0
         """
 
+        if justify not in ("left", "right", "center", "justify",
+                           "justify-all", "start", "end", "inherit",
+                           "match-parent", "initial", "unset"):
+            raise ValueError("Invalid value for justify parameter")
+
         formatter = fmt.DataFrameFormatter(self, buf=buf, columns=columns,
                                            col_space=col_space, na_rep=na_rep,
                                            formatters=formatters,

pandas/io/formats/format.py

@@ -80,8 +80,10 @@
         Width to wrap a line in characters, default no wrap"""
 
 justify_docstring = """
-    justify : {'left', 'right'}, default None
-        Left or right-justify the column labels. If None uses the option from
+    justify : {'left', 'right', 'center', 'justify',
+               'justify-all', 'start', 'end', 'inherit',
+               'match-parent', 'initial', 'unset'}, default None
+        How to justify the column labels. If None uses the option from
         the print configuration (controlled by set_option), 'right' out
         of the box."""