**Breaking**: data_kind: data is None and required now returns the 'empty' kind

pygmt/clib/session.py

@@ -1773,16 +1773,17 @@ def virtualfile_in(  # noqa: PLR0912
             if check_kind == "raster":
                 valid_kinds += ("grid", "image")
             elif check_kind == "vector":
-                valid_kinds += ("matrix", "vectors", "geojson")
+                valid_kinds += ("empty", "matrix", "vectors", "geojson")
             if kind not in valid_kinds:
                 raise GMTInvalidInput(
                     f"Unrecognized data type for {check_kind}: {type(data)}"
                 )
 
         # Decide which virtualfile_from_ function to use
         _virtualfile_from = {
-            "file": contextlib.nullcontext,
             "arg": contextlib.nullcontext,
+            "empty": self.virtualfile_from_vectors,
+            "file": contextlib.nullcontext,
             "geojson": tempfile_from_geojson,
             "grid": self.virtualfile_from_grid,
             "image": tempfile_from_image,
@@ -1803,15 +1804,15 @@ def virtualfile_in(  # noqa: PLR0912
                 )
                 warnings.warn(message=msg, category=RuntimeWarning, stacklevel=2)
             _data = (data,) if not isinstance(data, pathlib.PurePath) else (str(data),)
+        elif kind == "empty":
+            # data is None, so data must be given via x/y/z.
+            _data = [x, y]
+            if z is not None:
+                _data.append(z)
+            if extra_arrays:
+                _data.extend(extra_arrays)
         elif kind == "vectors":
-            if data is None:
-                # data is None, so data must be given via x/y/z.
-                _data = [x, y]
-                if z is not None:
-                    _data.append(z)
-                if extra_arrays:
-                    _data.extend(extra_arrays)
-            elif hasattr(data, "items") and not hasattr(data, "to_frame"):
+            if hasattr(data, "items") and not hasattr(data, "to_frame"):
                 # pandas.DataFrame or xarray.Dataset types.
                 # pandas.Series will be handled below like a 1-D numpy.ndarray.
                 _data = [array for _, array in data.items()]

pygmt/helpers/utils.py

@@ -190,7 +190,7 @@ def _check_encoding(
 def data_kind(
     data: Any, required: bool = True
 ) -> Literal[
-    "arg", "file", "geojson", "grid", "image", "matrix", "stringio", "vectors"
+    "arg", "empty", "file", "geojson", "grid", "image", "matrix", "stringio", "vectors"
 ]:
     r"""
     Check the kind of data that is provided to a module.
@@ -200,6 +200,8 @@ def data_kind(
 
     - ``"arg"``: ``data`` is ``None`` and ``required=False``, or bool, int, float,
       representing an optional argument, used for dealing with optional virtual files
+    - ``"empty"`: ``data`` is ``None`` and ``required=True``. It means the data is given
+      via a series of vectors like x/y/z
     - ``"file"``: a string or a :class:`pathlib.PurePath` object or a sequence of them,
       representing one or more file names
     - ``"geojson"``: a geo-like Python object that implements ``__geo_interface__``
@@ -209,10 +211,9 @@ def data_kind(
     - ``"stringio"``: a :class:`io.StringIO` object
     - ``"matrix"``: a 2-D array-like object that implements ``__array_interface__``
       (e.g., :class:`numpy.ndarray`)
-    - ``"vectors"``: ``data`` is ``None`` and ``required=True``, or any unrecognized
-      data. Common data types include, a :class:`pandas.DataFrame` object, a dictionary
-      with array-like values, a 1-D/3-D :class:`numpy.ndarray` object, or array-like
-      objects.
+    - ``"vectors"``: any unrecognized data. Common data types include, a
+      :class:`pandas.DataFrame` object, a dictionary with array-like values, a 1-D/3-D
+      :class:`numpy.ndarray` object, or array-like objects.
 
     Parameters
     ----------
@@ -242,6 +243,11 @@ def data_kind(
     >>> data_kind(data=None, required=False)
     'arg'
 
+    The "empty" kind:
+
+    >>> data_kind(data=None, required=True)
+    'empty'
+
     The "file" kind:
 
     >>> [data_kind(data=data) for data in ("file.txt", ("file1.txt", "file2.txt"))]
@@ -293,10 +299,10 @@ def data_kind(
     'vectors'
     >>> data_kind(data=pd.Series([1, 2, 3], name="x"))  # pd.Series
     'vectors'
-    >>> data_kind(data=None)
-    'vectors'
     """
     match data:
+        case None if required:  # No data provided and required=True.
+            kind = "empty"
         case str() | pathlib.PurePath():  # One file.
             kind = "file"
         case list() | tuple() if all(

pygmt/src/legend.py

@@ -91,7 +91,7 @@ def legend(
             kwargs["F"] = box
 
     kind = data_kind(spec)
-    if spec is not None and kind not in {"file", "stringio"}:
+    if kind not in {"empty", "file", "stringio"}:
         raise GMTInvalidInput(f"Unrecognized data type: {type(spec)}")
     if kind == "file" and is_nonstr_iter(spec):
         raise GMTInvalidInput("Only one legend specification file is allowed.")

pygmt/src/plot.py

@@ -206,7 +206,7 @@ def plot(self, data=None, x=None, y=None, size=None, direction=None, **kwargs):
 
     kind = data_kind(data)
     extra_arrays = []
-    if kind == "vectors":  # Add more columns for vectors input
+    if kind == "empty":  # Add more columns for vectors input
         # Parameters for vector styles
         if (
             kwargs.get("S") is not None

pygmt/src/plot3d.py

@@ -184,7 +184,7 @@ def plot3d(
     kind = data_kind(data)
     extra_arrays = []
 
-    if kind == "vectors":  # Add more columns for vectors input
+    if kind == "empty":  # Add more columns for vectors input
         # Parameters for vector styles
         if (
             kwargs.get("S") is not None

pygmt/src/text.py

@@ -196,7 +196,7 @@ def text_(  # noqa: PLR0912
         raise GMTInvalidInput("'text' can't be None or array when 'position' is given.")
     if textfiles is not None and text is not None:
         raise GMTInvalidInput("'text' can't be specified when 'textfiles' is given.")
-    if kind == "vectors" and text is None:
+    if kind == "empty" and text is None:
         raise GMTInvalidInput("Must provide text with x/y pairs.")
 
     # Arguments that can accept arrays.
@@ -220,7 +220,7 @@ def text_(  # noqa: PLR0912
 
     extra_arrays = []
     confdict = {}
-    if kind == "vectors":
+    if kind == "empty":
         for arg, flag, name in array_args:
             if is_nonstr_iter(arg):
                 kwargs["F"] += flag