clib.Session: Add the virtualfile_to_data method for creating virtual files for output

Author: seisman

doc/api/index.rst

@@ -293,6 +293,7 @@ conversion of Python variables to GMT virtual files:
     clib.Session.virtualfile_from_matrix
     clib.Session.virtualfile_from_vectors
     clib.Session.virtualfile_from_grid
+    clib.Session.virtualfile_to_data
 
 
 Low level access (these are mostly used by the :mod:`pygmt.clib` package):

pygmt/clib/session.py

@@ -1609,6 +1609,74 @@ def virtualfile_from_data(  # noqa: PLR0912
 
         return file_context
 
+    @contextlib.contextmanager
+    def virtualfile_to_data(
+        self, kind: Literal["dataset", "grid", None] = None, fname: str | None = None
+    ):
+        """
+        Create a virtual file for storing output data in a data container or yield the
+        actual file name.
+
+        Parameters
+        ----------
+        kind
+            The kind of data container to create. Valid values are ``"dataset"`` and
+            ``"grid"`` or ``None``. Ignored if ``fname`` is specified.
+        fname
+            If given, yield the actual file name instead of the virtual file name.
+
+        Yields
+        ------
+        vfile : str
+            Name of the virtual file or the output file name.
+
+        Examples
+        --------
+        >>> from pathlib import Path
+        >>> from pygmt.clib import Session
+        >>> from pygmt.datatypes import _GMT_DATASET, _GMT_GRID
+        >>> from pygmt.helpers import GMTTempFile
+        >>>
+        >>> # Create a virtual file for storing the output table.
+        >>> with GMTTempFile(suffix=".txt") as tmpfile:
+        ...     with open(tmpfile.name, mode="w") as fp:
+        ...         print("1.0 2.0 3.0 TEXT", file=fp)
+        ...     with Session() as lib:
+        ...         with lib.virtualfile_to_data(kind="dataset") as vouttbl:
+        ...             lib.call_module("read", f"{tmpfile.name} {vouttbl} -Td")
+        ...             ds = lib.read_virtualfile(vouttbl, kind="dataset")
+        >>> isinstance(ds.contents, _GMT_DATASET)
+        True
+        >>>
+        >>> # Create a virtual file for storing the output grid.
+        >>> with Session() as lib:
+        ...     with lib.virtualfile_to_data(kind="grid") as voutgrd:
+        ...         lib.call_module("read", f"@earth_relief_01d_g {voutgrd} -Tg")
+        ...         outgrd = lib.read_virtualfile(voutgrd, kind="grid")
+        >>> isinstance(outgrd.contents, _GMT_GRID)
+        True
+        >>>
+        >>> # Write data to file without creating a virtual file
+        >>> with GMTTempFile(suffix=".nc") as tmpfile:
+        ...     with Session() as lib:
+        ...         with lib.virtualfile_to_data(fname=tmpfile.name) as voutgrd:
+        ...             lib.call_module("read", f"@earth_relief_01d_g {voutgrd} -Tg")
+        ...             assert voutgrd == tmpfile.name
+        ...             assert Path(voutgrd).stat().st_size > 0
+        """
+        # If fname is given, yield the output file name.
+        if fname is not None:
+            yield fname
+        # Otherwise, create a virtual file for storing the output data.
+        else:
+            # Determine the family and geometry from kind
+            family, geometry = {
+                "grid": ("GMT_IS_GRID", "GMT_IS_SURFACE"),
+                "dataset": ("GMT_IS_DATASET", "GMT_IS_PLP"),
+            }[kind]
+            with self.open_virtualfile(family, geometry, "GMT_OUT", None) as vfile:
+                yield vfile
+
     def read_virtualfile(
         self, vfname: str, kind: Literal["dataset", "grid", None] = None
     ):