Omit hidden DataFrame indices from first-row headers

README.md

@@ -162,6 +162,9 @@ or `showindex=False`. To add a custom row index column, pass
 
 ```
 
+With `headers="firstrow"`, hiding a DataFrame's row index also omits its
+first index value from the header.
+
 ### Table format
 
 There is more than one way to format a table in plain text. The third

tabulate/__init__.py

@@ -1574,6 +1574,7 @@ def _normalize_tabular_data(tabular_data, headers, showindex="default"):
             headers = list(map(str, range(len(rows[0]))))
 
     # take headers from the first row if necessary
+    index_header_from_firstrow = headers == "firstrow" and index is not None
     if headers == "firstrow" and len(rows) > 0:
         if index is not None:
             headers = [index[0]] + list(rows[0])
@@ -1602,7 +1603,8 @@ def _normalize_tabular_data(tabular_data, headers, showindex="default"):
             index = list(range(len(rows)))
         rows = _prepend_row_index(rows, index)
     elif showindex == "never" or (not _bool(showindex) and not showindex_is_a_str):
-        pass
+        if index_header_from_firstrow:
+            headers = headers[1:]
 
     # pad with empty headers for initial columns if necessary
     headers_pad = 0

test/test_dataframe_firstrow.py

@@ -0,0 +1,38 @@
+"""First-row headers must respect whether the DataFrame index is shown."""
+
+import pytest
+
+from tabulate import tabulate
+
+
+@pytest.mark.parametrize("tablefmt", ["simple", "grid", "html"])
+@pytest.mark.parametrize("row_count", [0, 1, 2])
+@pytest.mark.parametrize("showindex", [False, "never"])
+def test_dataframe_firstrow_without_index(tablefmt, row_count, showindex):
+    pandas = pytest.importorskip("pandas")
+    rows = [["Name", "Age"]] + [[f"Person {i}", i] for i in range(row_count)]
+    frame = pandas.DataFrame(rows, index=["row label"] + list(range(row_count)))
+
+    assert tabulate(frame, headers="firstrow", showindex=showindex, tablefmt=tablefmt) == tabulate(
+        rows, headers="firstrow", tablefmt=tablefmt
+    )
+
+
+@pytest.mark.parametrize("showindex", [True, "always", "default"])
+def test_dataframe_firstrow_with_index(showindex):
+    pandas = pytest.importorskip("pandas")
+    frame = pandas.DataFrame([["Name", "Age"], ["Alice", 30]], index=["row label", "first"])
+
+    assert tabulate(frame, headers="firstrow", showindex=showindex) == tabulate(
+        [["row label", "Name", "Age"], ["first", "Alice", 30]], headers="firstrow"
+    )
+
+
+def test_dataframe_firstrow_numpy_false():
+    numpy = pytest.importorskip("numpy")
+    pandas = pytest.importorskip("pandas")
+    rows = [["Name", "Age"], ["Alice", 30]]
+
+    assert tabulate(
+        pandas.DataFrame(rows), headers="firstrow", showindex=numpy.bool_(False)
+    ) == tabulate(rows, headers="firstrow")