Let kwargs_to_strings work with default values and postional arguments

pygmt/helpers/decorators.py

@@ -636,7 +636,6 @@ def kwargs_to_strings(**conversions):
 
     Examples
     --------
-
     >>> @kwargs_to_strings(
     ...     R="sequence", i="sequence_comma", files="sequence_space"
     ... )
@@ -686,58 +685,97 @@ def kwargs_to_strings(**conversions):
     ...     ]
     ... )
     {'R': '2005-01-01T08:00:00.000000000/2015-01-01T12:00:00.123456'}
+    >>> # Here is a more realistic example
+    >>> # See https://github.com/GenericMappingTools/pygmt/issues/2361
+    >>> @kwargs_to_strings(
+    ...     files="sequence_space",
+    ...     offset="sequence",
+    ...     R="sequence",
+    ...     i="sequence_comma",
+    ... )
+    ... def module(files, offset=("-54p", "-54p"), **kwargs):
+    ...     "A module that prints the arguments it received"
+    ...     print(files, end=" ")
+    ...     print(offset, end=" ")
+    ...     print("{", end="")
+    ...     print(
+    ...         ", ".join(f"'{k}': {repr(kwargs[k])}" for k in sorted(kwargs)),
+    ...         end="",
+    ...     )
+    ...     print("}")
+    >>> module(files=["data1.txt", "data2.txt"])
+    data1.txt data2.txt -54p/-54p {}
+    >>> module(["data1.txt", "data2.txt"])
+    data1.txt data2.txt -54p/-54p {}
+    >>> module(files=["data1.txt", "data2.txt"], offset=("20p", "20p"))
+    data1.txt data2.txt 20p/20p {}
+    >>> module(["data1.txt", "data2.txt"], ("20p", "20p"))
+    data1.txt data2.txt 20p/20p {}
+    >>> module(["data1.txt", "data2.txt"], ("20p", "20p"), R=[1, 2, 3, 4])
+    data1.txt data2.txt 20p/20p {'R': '1/2/3/4'}
     """
-    valid_conversions = [
-        "sequence",
-        "sequence_comma",
-        "sequence_plus",
-        "sequence_space",
-    ]
-
-    for arg, fmt in conversions.items():
-        if fmt not in valid_conversions:
-            raise GMTInvalidInput(
-                f"Invalid conversion type '{fmt}' for argument '{arg}'."
-            )
-
     separators = {
         "sequence": "/",
         "sequence_comma": ",",
         "sequence_plus": "+",
         "sequence_space": " ",
     }
 
+    for arg, fmt in conversions.items():
+        if fmt not in separators:
+            raise GMTInvalidInput(
+                f"Invalid conversion type '{fmt}' for argument '{arg}'."
+            )
+
     # Make the actual decorator function
     def converter(module_func):
         """
         The decorator that creates our new function with the conversions.
         """
+        sig = signature(module_func)
 
         @functools.wraps(module_func)
         def new_module(*args, **kwargs):
             """
             New module instance that converts the arguments first.
             """
+            # Inspired by https://stackoverflow.com/a/69170441
+            bound = sig.bind(*args, **kwargs)
+            bound.apply_defaults()
+
             for arg, fmt in conversions.items():
-                if arg in kwargs:
-                    value = kwargs[arg]
-                    issequence = fmt in separators
-                    if issequence and is_nonstr_iter(value):
-                        for index, item in enumerate(value):
-                            try:
-                                # check if there is a space " " when converting
-                                # a pandas.Timestamp/xr.DataArray to a string.
-                                # If so, use np.datetime_as_string instead.
-                                assert " " not in str(item)
-                            except AssertionError:
-                                # convert datetime-like item to ISO 8601
-                                # string format like YYYY-MM-DDThh:mm:ss.ffffff
-                                value[index] = np.datetime_as_string(
-                                    np.asarray(item, dtype=np.datetime64)
-                                )
-                        kwargs[arg] = separators[fmt].join(f"{item}" for item in value)
+                # The arg may be in args or kwargs
+                if arg in bound.arguments:
+                    value = bound.arguments[arg]
+                elif arg in bound.arguments.get("kwargs"):
+                    value = bound.arguments["kwargs"][arg]
+                else:
+                    continue
+
+                issequence = fmt in separators
+                if issequence and is_nonstr_iter(value):
+                    for index, item in enumerate(value):
+                        try:
+                            # check if there is a space " " when converting
+                            # a pandas.Timestamp/xr.DataArray to a string.
+                            # If so, use np.datetime_as_string instead.
+                            assert " " not in str(item)
+                        except AssertionError:
+                            # convert datetime-like item to ISO 8601
+                            # string format like YYYY-MM-DDThh:mm:ss.ffffff
+                            value[index] = np.datetime_as_string(
+                                np.asarray(item, dtype=np.datetime64)
+                            )
+                    newvalue = separators[fmt].join(f"{item}" for item in value)
+                    # Changes in bound.arguments will reflect in bound.args
+                    # and bound.kwargs.
+                    if arg in bound.arguments:
+                        bound.arguments[arg] = newvalue
+                    elif arg in bound.arguments.get("kwargs"):
+                        bound.arguments["kwargs"][arg] = newvalue
+
             # Execute the original function and return its output
-            return module_func(*args, **kwargs)
+            return module_func(*bound.args, **bound.kwargs)
 
         return new_module