Fix csvformat header options on empty input

CHANGELOG.rst

@@ -1,6 +1,8 @@
 Unreleased
 ----------
 
+-  fix: :doc:`/scripts/csvformat` accepts empty input with :code:`--skip-header` and :code:`--no-header-row`, including when :code:`--skip-lines` consumes the entire input.
+
 -  feat: :doc:`/scripts/csvcut` adds an :code:`--ignore-unknown-columns` option to skip identifiers in :code:`-c/--columns` that do not match a column in the input.
 -  feat: :doc:`/scripts/csvclean` adds a :code:`--remove-empty-columns` option to remove empty columns from standard output.
 -  feat: :doc:`/scripts/in2csv` guesses the ``ndjson`` format for files with :code:`.ndjson`, :code:`.jsonl` and :code:`.jl` extensions.

csvkit/utilities/csvformat.py

@@ -91,12 +91,14 @@ def main(self):
             reader = agate.csv.reader(self.skip_lines(), **self.reader_kwargs)
             if self.args.no_header_row:
                 # Peek at a row to get the number of columns.
-                _row = next(reader)
+                _row = next(reader, None)
+                if _row is None:
+                    return
                 headers = make_default_headers(len(_row))
                 reader = itertools.chain([headers, _row], reader)
 
             if self.args.skip_header:
-                next(reader)
+                next(reader, None)
 
             writer.writerows(reader)
 

tests/test_utilities/test_csvformat.py

@@ -24,6 +24,19 @@ def test_skip_header(self):
             '1,2,3',
         ])
 
+    def test_empty_with_header_options(self):
+        for options in (['--skip-header'], ['--no-header-row'],
+                        ['--no-header-row', '--skip-header']):
+            with self.subTest(options=options):
+                with stdin_as_string(io.BytesIO(b'')):
+                    self.assertLines(options, [])
+
+    def test_skip_all_lines_with_header_options(self):
+        for options in (['--skip-header'], ['--no-header-row'],
+                        ['--no-header-row', '--skip-header']):
+            with self.subTest(options=options):
+                self.assertLines(options + ['--skip-lines', '2', 'examples/dummy.csv'], [])
+
     def test_skip_header_no_header_row(self):
         self.assertLines(['--no-header-row', '--skip-header', 'examples/no_header_row.csv'], [
             '1,2,3',