[ENH] Added ReprMixin to share __repr__ formatting (#1595)

* Reference Issue:  Fixes #1591 
* New Tests Added: No
* Documentation Updated: Yes (docstring)
* Change Log Entry: Adds `ReprMixin` in `utils`

Author: JATAYU000

openml/utils.py

@@ -2,12 +2,20 @@
 from __future__ import annotations
 
 import contextlib
+import re
 import shutil
 import warnings
-from collections.abc import Callable, Mapping, Sized
+from abc import ABC, abstractmethod
+from collections.abc import Callable, Iterable, Mapping, Sequence, Sized
 from functools import wraps
 from pathlib import Path
-from typing import TYPE_CHECKING, Any, Literal, TypeVar, overload
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Literal,
+    TypeVar,
+    overload,
+)
 from typing_extensions import ParamSpec
 
 import numpy as np
@@ -470,3 +478,57 @@ def update(self, length: int) -> None:
         self._progress_bar.update(length)
         if self._progress_bar.total <= self._progress_bar.n:
             self._progress_bar.close()
+
+
+class ReprMixin(ABC):
+    """A mixin class that provides a customizable string representation for OpenML objects.
+
+    This mixin standardizes the __repr__ output format across OpenML classes.
+    Classes inheriting from this mixin should implement the
+    _get_repr_body_fields method to specify which fields to display.
+    """
+
+    def __repr__(self) -> str:
+        body_fields = self._get_repr_body_fields()
+        return self._apply_repr_template(body_fields)
+
+    @abstractmethod
+    def _get_repr_body_fields(self) -> Sequence[tuple[str, str | int | list[str] | None]]:
+        """Collect all information to display in the __repr__ body.
+
+        Returns
+        -------
+        body_fields : List[Tuple[str, Union[str, int, List[str]]]]
+            A list of (name, value) pairs to display in the body of the __repr__.
+            E.g.: [('metric', 'accuracy'), ('dataset', 'iris')]
+            If value is a List of str, then each item of the list will appear in a separate row.
+        """
+        # Should be implemented in the base class.
+
+    def _apply_repr_template(
+        self,
+        body_fields: Iterable[tuple[str, str | int | list[str] | None]],
+    ) -> str:
+        """Generates the header and formats the body for string representation of the object.
+
+        Parameters
+        ----------
+        body_fields: List[Tuple[str, str]]
+           A list of (name, value) pairs to display in the body of the __repr__.
+        """
+        # We add spaces between capitals, e.g. ClassificationTask -> Classification Task
+        name_with_spaces = re.sub(
+            r"(\w)([A-Z])",
+            r"\1 \2",
+            self.__class__.__name__[len("OpenML") :],
+        )
+        header_text = f"OpenML {name_with_spaces}"
+        header = f"{header_text}\n{'=' * len(header_text)}\n"
+
+        _body_fields: list[tuple[str, str | int | list[str]]] = [
+            (k, "None" if v is None else v) for k, v in body_fields
+        ]
+        longest_field_name_length = max(len(name) for name, _ in _body_fields)
+        field_line_format = f"{{:.<{longest_field_name_length}}}: {{}}"
+        body = "\n".join(field_line_format.format(name, value) for name, value in _body_fields)
+        return header + body