Move the parser function into _common.py

pygmt/src/_common.py

@@ -3,8 +3,9 @@
 """
 
 from pathlib import Path
-from typing import Any
+from typing import Any, Literal
 
+from pygmt.exceptions import GMTInvalidInput
 from pygmt.src.which import which
 
 
@@ -39,3 +40,59 @@ def _data_geometry_is_point(data: Any, kind: str) -> bool:
         except FileNotFoundError:
             pass
     return False
+
+
+def _parse_coastline_resolution(
+    resolution: Literal["auto", "full", "high", "intermediate", "low", "crude", None],
+    allow_auto: bool = False,
+) -> str | None:
+    """
+    Parse the resolution parameter for coastline-related functions.
+
+    Parameters
+    ----------
+    resolution
+        The resolution of the coastline dataset to use. The available resolutions from
+        highest to lowest are: ``"full"``, ``"high"``, ``"intermediate"``, ``"low"``,
+        and ``"crude"``, which drops by 80% between levels.
+    allow_auto
+        Whether to allow the ``"auto"`` resolution.
+
+    Returns
+    -------
+    str or None
+        The parsed resolution value.
+
+    Raises
+    ------
+    GMTInvalidInput
+        If the resolution is invalid.
+
+    Examples
+    --------
+    >>> _parse_coastline_resolution("full")
+    "f"
+    >>> _parse_coastline_resolution("f")
+    "f"
+    >>> _parse_coastline_resolution("auto", allow_auto=True)
+    "a"
+    >>> _parse_coastline_resolution("invalid")
+    pygmt.exceptions.GMTInvalidInput: Invalid resolution: invalid. Valid values are ...
+    >>> _parse_coastline_resolution(None)
+    None
+    >>> _parse_coastline_resolution("auto")
+    pygmt.exceptions.GMTInvalidInput: Invalid resolution: auto. Valid values are ...
+    """
+    if resolution is None:
+        return None
+
+    valid_resolutions = {"full", "high", "intermediate", "low", "crude"}
+    if allow_auto:
+        valid_resolutions.add("auto")
+    if resolution not in {*valid_resolutions, *[res[0] for res in valid_resolutions]}:
+        msg = (
+            f"Invalid resolution: {resolution}."
+            f"Valid values are {', '.join(valid_resolutions)}."
+        )
+        raise GMTInvalidInput(msg)
+    return resolution[0]

pygmt/src/coast.py

@@ -13,6 +13,7 @@
     kwargs_to_strings,
     use_alias,
 )
+from pygmt.src._common import _parse_coastline_resolution
 
 __doctest_skip__ = ["coast"]
 
@@ -41,8 +42,8 @@
 def coast(
     self,
     resolution: Literal[
-        "auto", "full", "high", "intermediate", "low", "crude"
-    ] = "auto",
+        "auto", "full", "high", "intermediate", "low", "crude", None
+    ] = None,
     **kwargs,
 ):
     r"""
@@ -208,9 +209,8 @@ def coast(
             """At least one of the following parameters must be specified:
             lakes, land, water, rivers, borders, dcw, Q, or shorelines"""
         )
-
-    # Alias 'resolution' to "D".
-    kwargs["D"] = resolution[0]
-
+    kwargs["D"] = kwargs.get(
+        "D", _parse_coastline_resolution(resolution, allow_auto=True)
+    )
     with Session() as lib:
         lib.call_module(module="coast", args=build_arg_list(kwargs))

pygmt/src/grdlandmask.py

@@ -8,6 +8,7 @@
 from pygmt.clib import Session
 from pygmt.exceptions import GMTInvalidInput
 from pygmt.helpers import build_arg_list, fmt_docstring, kwargs_to_strings, use_alias
+from pygmt.src._common import _parse_coastline_resolution
 
 __doctest_skip__ = ["grdlandmask"]
 
@@ -26,7 +27,7 @@
 @kwargs_to_strings(I="sequence", R="sequence", N="sequence", E="sequence")
 def grdlandmask(
     outgrid: str | None = None,
-    resolution: Literal["full", "high", "intermediate", "low", "crude"] = "low",
+    resolution: Literal["full", "high", "intermediate", "low", "crude", None] = None,
     **kwargs,
 ) -> xr.DataArray | None:
     r"""
@@ -99,8 +100,8 @@ def grdlandmask(
     if kwargs.get("I") is None or kwargs.get("R") is None:
         raise GMTInvalidInput("Both 'region' and 'spacing' must be specified.")
 
-    # Alias "resolution" to "D"
-    kwargs["D"] = resolution[0]
+    kwargs["D"] = kwargs.get("D", _parse_coastline_resolution(resolution))
+
     with Session() as lib:
         with lib.virtualfile_out(kind="grid", fname=outgrid) as voutgrd:
             kwargs["G"] = voutgrd

pygmt/src/select.py

@@ -14,6 +14,7 @@
     use_alias,
     validate_output_table_type,
 )
+from pygmt.src._common import _parse_coastline_resolution
 
 __doctest_skip__ = ["select"]
 
@@ -47,7 +48,7 @@ def select(
     data=None,
     output_type: Literal["pandas", "numpy", "file"] = "pandas",
     outfile: str | None = None,
-    resolution: Literal["full", "high", "intermediate", "low", "crude"] = "low",
+    resolution: Literal["full", "high", "intermediate", "low", "crude", None] = None,
     **kwargs,
 ) -> pd.DataFrame | np.ndarray | None:
     r"""
@@ -203,7 +204,7 @@ def select(
     >>> out = pygmt.select(data=ship_data, region=[246, 247, 20, 21])
     """
     # Alias "resolution" to "D"
-    kwargs["D"] = resolution[0]
+    kwargs["D"] = kwargs.get("D", _parse_coastline_resolution(resolution))
 
     output_type = validate_output_table_type(output_type, outfile=outfile)