From b83ddc4146548390bd030b155db5e07b587e4139 Mon Sep 17 00:00:00 2001
From: Chris Stadler <chrisstadler@gmail.com>
Date: Thu, 11 Jul 2019 12:24:00 -0400
Subject: [PATCH 1/2] BUG: Accept empty dataframes in DataFrame.to_parquet

---
 pandas/io/parquet.py            |  2 +-
 pandas/tests/io/test_parquet.py | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/pandas/io/parquet.py b/pandas/io/parquet.py
index 3db05b94e5dce..a2502df45169f 100644
--- a/pandas/io/parquet.py
+++ b/pandas/io/parquet.py
@@ -55,7 +55,7 @@ def validate_dataframe(df):
             raise ValueError("to_parquet only supports IO with DataFrames")
 
         # must have value column names (strings only)
-        if df.columns.inferred_type not in {"string", "unicode"}:
+        if df.columns.inferred_type not in {"string", "unicode", "empty"}:
             raise ValueError("parquet must have string column names")
 
         # index level names must be strings
diff --git a/pandas/tests/io/test_parquet.py b/pandas/tests/io/test_parquet.py
index 6ac2e9cd65a27..b2f55a43047cc 100644
--- a/pandas/tests/io/test_parquet.py
+++ b/pandas/tests/io/test_parquet.py
@@ -471,6 +471,10 @@ def test_partition_cols_supported(self, pa, df_full):
             assert len(dataset.partitions.partition_names) == 2
             assert dataset.partitions.partition_names == set(partition_cols)
 
+    def test_empty_dataframe(self, pa):
+        df = pd.DataFrame()
+        check_round_trip(df, pa)
+
 
 class TestParquetFastParquet(Base):
     @td.skip_if_no("fastparquet", min_version="0.2.1")
@@ -566,3 +570,9 @@ def test_error_on_using_partition_cols_and_partition_on(self, fp, df_full):
                     partition_on=partition_cols,
                     partition_cols=partition_cols,
                 )
+
+    def test_empty_dataframe(self, fp):
+        df = pd.DataFrame()
+        expected = df.copy()
+        expected.index.name = "index"
+        check_round_trip(df, fp, expected=expected)

From ae8e024f5c4470eb2e9524d14bf61a46991f5715 Mon Sep 17 00:00:00 2001
From: Chris Stadler <chrisstadler@gmail.com>
Date: Thu, 11 Jul 2019 14:24:54 -0400
Subject: [PATCH 2/2] Update whatsnew and add issue number to tests

---
 doc/source/whatsnew/v0.25.0.rst | 1 +
 pandas/tests/io/test_parquet.py | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/doc/source/whatsnew/v0.25.0.rst b/doc/source/whatsnew/v0.25.0.rst
index ebe8b4770f6aa..f85449bf206e4 100644
--- a/doc/source/whatsnew/v0.25.0.rst
+++ b/doc/source/whatsnew/v0.25.0.rst
@@ -1101,6 +1101,7 @@ I/O
 - Fixed bug in :func:`DataFrame.to_excel()` where custom objects (i.e. `PeriodIndex`) inside merged cells were not being converted into types safe for the Excel writer (:issue:`27006`)
 - Bug in :meth:`read_hdf` where reading a timezone aware :class:`DatetimeIndex` would raise a ``TypeError`` (:issue:`11926`)
 - Bug in :meth:`to_msgpack` and :meth:`read_msgpack` which would raise a ``ValueError`` rather than a ``FileNotFoundError`` for an invalid path (:issue:`27160`)
+- Fixed bug in :meth:`DataFrame.to_parquet` which would raise a ``ValueError`` when the dataframe had no columns (:issue:`27339`)
 
 Plotting
 ^^^^^^^^
diff --git a/pandas/tests/io/test_parquet.py b/pandas/tests/io/test_parquet.py
index b2f55a43047cc..a04fb9fd50257 100644
--- a/pandas/tests/io/test_parquet.py
+++ b/pandas/tests/io/test_parquet.py
@@ -472,6 +472,7 @@ def test_partition_cols_supported(self, pa, df_full):
             assert dataset.partitions.partition_names == set(partition_cols)
 
     def test_empty_dataframe(self, pa):
+        # GH #27339
         df = pd.DataFrame()
         check_round_trip(df, pa)
 
@@ -572,6 +573,7 @@ def test_error_on_using_partition_cols_and_partition_on(self, fp, df_full):
                 )
 
     def test_empty_dataframe(self, fp):
+        # GH #27339
         df = pd.DataFrame()
         expected = df.copy()
         expected.index.name = "index"