From e81e96ec820dc035598c00b6c0fd04b2238ad99b Mon Sep 17 00:00:00 2001
From: Pietro Battiston <me@pietrobattiston.it>
Date: Wed, 6 Dec 2017 20:27:49 +0100
Subject: [PATCH] BUG: do not escape empty placeholder in to_latex()

closes #18667
---
 doc/source/whatsnew/v0.22.0.txt          |  2 +-
 pandas/io/formats/format.py              |  2 +-
 pandas/tests/io/formats/test_to_latex.py | 32 ++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/doc/source/whatsnew/v0.22.0.txt b/doc/source/whatsnew/v0.22.0.txt
index d34c1f3535509..ca7c43d1f2b31 100644
--- a/doc/source/whatsnew/v0.22.0.txt
+++ b/doc/source/whatsnew/v0.22.0.txt
@@ -302,7 +302,7 @@ I/O
 - Bug in :func:`read_msgpack` with a non existent file is passed in Python 2 (:issue:`15296`)
 - Bug in :func:`read_csv` where a ``MultiIndex`` with duplicate columns was not being mangled appropriately (:issue:`18062`)
 - Bug in :func:`read_sas` where a file with 0 variables gave an ``AttributeError`` incorrectly. Now it gives an ``EmptyDataError`` (:issue:`18184`)
--
+- Bug in :func:`DataFrame.to_latex()` where pairs of braces meant to serve as invisible placeholders were escaped (:issue:`18667`)
 -
 
 Plotting
diff --git a/pandas/io/formats/format.py b/pandas/io/formats/format.py
index 8f25eb3af70cd..4b7f4de12bb65 100644
--- a/pandas/io/formats/format.py
+++ b/pandas/io/formats/format.py
@@ -967,7 +967,7 @@ def get_col_type(dtype):
                          .replace('#', '\\#').replace('{', '\\{')
                          .replace('}', '\\}').replace('~', '\\textasciitilde')
                          .replace('^', '\\textasciicircum').replace('&', '\\&')
-                         if x else '{}') for x in row]
+                         if (x and x != '{}') else '{}') for x in row]
             else:
                 crow = [x if x else '{}' for x in row]
             if self.bold_rows and self.fmt.index:
diff --git a/pandas/tests/io/formats/test_to_latex.py b/pandas/tests/io/formats/test_to_latex.py
index 35ef5a1cf5c72..549a1e1ce316a 100644
--- a/pandas/tests/io/formats/test_to_latex.py
+++ b/pandas/tests/io/formats/test_to_latex.py
@@ -536,3 +536,35 @@ def test_to_latex_no_bold_rows(self):
 \end{tabular}
 """
         assert observed == expected
+
+    @pytest.mark.parametrize('name0', [None, 'named'])
+    @pytest.mark.parametrize('name1', [None, 'named'])
+    @pytest.mark.parametrize('axes', [[0], [1], [0, 1]])
+    def test_to_latex_multiindex_names(self, name0, name1, axes):
+        # GH 18667
+        names = [name0, name1]
+        mi = pd.MultiIndex.from_product([[1, 2], [3, 4]])
+        df = pd.DataFrame(-1, index=mi.copy(), columns=mi.copy())
+        for idx in axes:
+            df.axes[idx].names = names
+
+        idx_names = tuple(n or '{}' for n in names)
+        idx_names_row = ('%s & %s &    &    &    &    \\\\\n' % idx_names
+                         if (0 in axes and any(names)) else '')
+        placeholder = '{}' if any(names) and 1 in axes else ' '
+        col_names = [n if (bool(n) and 1 in axes) else placeholder
+                     for n in names]
+        observed = df.to_latex()
+        expected = r"""\begin{tabular}{llrrrr}
+\toprule
+  & %s & \multicolumn{2}{l}{1} & \multicolumn{2}{l}{2} \\
+  & %s &  3 &  4 &  3 &  4 \\
+%s\midrule
+1 & 3 & -1 & -1 & -1 & -1 \\
+  & 4 & -1 & -1 & -1 & -1 \\
+2 & 3 & -1 & -1 & -1 & -1 \\
+  & 4 & -1 & -1 & -1 & -1 \\
+\bottomrule
+\end{tabular}
+""" % tuple(list(col_names) + [idx_names_row])
+        assert observed == expected