BUG: DataFrame.to_markdown with an empty frame (#38406)

Author: arw2019

ci/deps/azure-38.yaml

@@ -17,4 +17,4 @@ dependencies:
   - python-dateutil
   - nomkl
   - pytz
-  - tabulate==0.8.3
+  - tabulate==0.8.7

doc/source/getting_started/install.rst

@@ -283,7 +283,7 @@ pyreadstat                                   SPSS files (.sav) reading
 pyxlsb                    1.0.6              Reading for xlsb files
 qtpy                                         Clipboard I/O
 s3fs                      0.4.0              Amazon S3 access
-tabulate                  0.8.3              Printing in Markdown-friendly format (see `tabulate`_)
+tabulate                  0.8.7              Printing in Markdown-friendly format (see `tabulate`_)
 xarray                    0.12.3             pandas-like API for N-dimensional data
 xclip                                        Clipboard I/O on linux
 xlrd                      1.2.0              Excel reading

doc/source/whatsnew/v1.3.0.rst

@@ -37,7 +37,76 @@ These are bug fixes that might have notable behavior changes.
 
 Increased minimum versions for dependencies
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
+Some minimum supported versions of dependencies were updated.
+If installed, we now require:
+
++-----------------+-----------------+----------+---------+
+| Package         | Minimum Version | Required | Changed |
++=================+=================+==========+=========+
+| numpy           | 1.16.5          |    X     |         |
++-----------------+-----------------+----------+---------+
+| pytz            | 2017.3          |    X     |         |
++-----------------+-----------------+----------+---------+
+| python-dateutil | 2.7.3           |    X     |         |
++-----------------+-----------------+----------+---------+
+| bottleneck      | 1.2.1           |          |         |
++-----------------+-----------------+----------+---------+
+| numexpr         | 2.6.8           |          |         |
++-----------------+-----------------+----------+---------+
+| pytest (dev)    | 5.0.1           |          |         |
++-----------------+-----------------+----------+---------+
+| mypy (dev)      | 0.782           |          |         |
++-----------------+-----------------+----------+---------+
+
+For `optional libraries <https://dev.pandas.io/docs/install.html#dependencies>`_ the general recommendation is to use the latest version.
+The following table lists the lowest version per library that is currently being tested throughout the development of pandas.
+Optional libraries below the lowest tested version may still work, but are not considered supported.
+
++-----------------+-----------------+---------+
+| Package         | Minimum Version | Changed |
++=================+=================+=========+
+| beautifulsoup4  | 4.6.0           |         |
++-----------------+-----------------+---------+
+| fastparquet     | 0.3.2           |         |
++-----------------+-----------------+---------+
+| fsspec          | 0.7.4           |         |
++-----------------+-----------------+---------+
+| gcsfs           | 0.6.0           |         |
++-----------------+-----------------+---------+
+| lxml            | 4.3.0           |         |
++-----------------+-----------------+---------+
+| matplotlib      | 2.2.3           |         |
++-----------------+-----------------+---------+
+| numba           | 0.46.0          |         |
++-----------------+-----------------+---------+
+| openpyxl        | 2.6.0           |         |
++-----------------+-----------------+---------+
+| pyarrow         | 0.15.0          |         |
++-----------------+-----------------+---------+
+| pymysql         | 0.7.11          |         |
++-----------------+-----------------+---------+
+| pytables        | 3.5.1           |         |
++-----------------+-----------------+---------+
+| s3fs            | 0.4.0           |         |
++-----------------+-----------------+---------+
+| scipy           | 1.2.0           |         |
++-----------------+-----------------+---------+
+| sqlalchemy      | 1.2.8           |         |
++-----------------+-----------------+---------+
+| tabulate        | 0.8.7           |    X    |
++-----------------+-----------------+---------+
+| xarray          | 0.12.0          |         |
++-----------------+-----------------+---------+
+| xlrd            | 1.2.0           |         |
++-----------------+-----------------+---------+
+| xlsxwriter      | 1.0.2           |         |
++-----------------+-----------------+---------+
+| xlwt            | 1.3.0           |         |
++-----------------+-----------------+---------+
+| pandas-gbq      | 0.12.0          |         |
++-----------------+-----------------+---------+
+
+See :ref:`install.dependencies` and :ref:`install.optional_dependencies` for more.
 
 .. _whatsnew_130.api.other:
 

pandas/compat/_optional.py

@@ -24,7 +24,7 @@
     "scipy": "1.2.0",
     "sqlalchemy": "1.2.8",
     "tables": "3.5.1",
-    "tabulate": "0.8.3",
+    "tabulate": "0.8.7",
     "xarray": "0.12.3",
     "xlrd": "1.2.0",
     "xlwt": "1.3.0",

pandas/tests/io/formats/test_to_markdown.py

@@ -18,6 +18,17 @@ def test_simple():
     )
 
 
+def test_empty_frame():
+    buf = StringIO()
+    df = pd.DataFrame({"id": [], "first_name": [], "last_name": []}).set_index("id")
+    df.to_markdown(buf=buf)
+    result = buf.getvalue()
+    assert result == (
+        "| id   | first_name   | last_name   |\n"
+        "|------|--------------|-------------|"
+    )
+
+
 def test_other_tablefmt():
     buf = StringIO()
     df = pd.DataFrame([1, 2, 3])