FIX: Handle single class edge case in balanced_accuracy_score(adjusted=True) - #34937

sklearn/metrics/_classification.py:2884:1: SyntaxError: Expected class, function definition or async function definition after decorator
     |
2882 |     prefer_skip_nested_validation=True,
2883 | )
2884 | (y_true, y_pred, *, sample_weight=None, adjusted=False):
     | ^
2885 |     """Compute the balanced accuracy.
     |

sklearn/metrics/_classification.py:2884:1: SyntaxError: Only single target (not tuple) can be annotated
     |
2882 |     prefer_skip_nested_validation=True,
2883 | )
2884 | (y_true, y_pred, *, sample_weight=None, adjusted=False):
     | ^
2885 |     """Compute the balanced accuracy.
     |

sklearn/metrics/_classification.py:2884:19: SyntaxError: Expected an expression
     |
2882 |     prefer_skip_nested_validation=True,
2883 | )
2884 | (y_true, y_pred, *, sample_weight=None, adjusted=False):
     |                   ^
2885 |     """Compute the balanced accuracy.
     |

sklearn/metrics/_classification.py:2884:34: SyntaxError: Expected ',', found '='
     |
2882 |     prefer_skip_nested_validation=True,
2883 | )
2884 | (y_true, y_pred, *, sample_weight=None, adjusted=False):
     |                                  ^
2885 |     """Compute the balanced accuracy.
     |

sklearn/metrics/_classification.py:2884:49: SyntaxError: Expected ',', found '='
     |
2882 |     prefer_skip_nested_validation=True,
2883 | )
2884 | (y_true, y_pred, *, sample_weight=None, adjusted=False):
     |                                                 ^
2885 |     """Compute the balanced accuracy.
     |

sklearn/metrics/_classification.py:2884:57: SyntaxError: Expected an expression
     |
2882 |     prefer_skip_nested_validation=True,
2883 | )
2884 | (y_true, y_pred, *, sample_weight=None, adjusted=False):
     |                                                         ^
2885 |     """Compute the balanced accuracy.
2886 |
2887 |     The balanced accuracy in binary and multiclass classification problems to
     |

sklearn/metrics/_classification.py:2885:1: SyntaxError: Unexpected indentation
     |
2883 | )
2884 | (y_true, y_pred, *, sample_weight=None, adjusted=False):
2885 |     """Compute the balanced accuracy.
     | ^
2886 |
2887 |     The balanced accuracy in binary and multiclass classification problems to
     |

sklearn/metrics/_classification.py:2972:5: SyntaxError: Expected an indented block after `if` statement
     |
2970 |     score = xp.mean(per_class)
2971 |     if adjusted:
2972 |     n_classes = per_class.shape[0]
     |     ^
2973 |     if n_classes == 1:
2974 |         raise ValueError(
     |

sklearn/metrics/_classification.py:2985:1: SyntaxError: Expected a statement
     |
2985 | @validate_params(
     | ^
2986 |     {
2987 |         "y_true": ["array-like", "sparse matrix"],
     |

Found 9 errors.

error: Failed to parse sklearn/metrics/_classification.py:2884:1: Expected class, function definition or async function definition after decorator
960 files already formatted

 INFO Checking project configured at `/home/runner/work/scikit-learn/scikit-learn/pyproject.toml`
ERROR Parse error: Expected class, function definition or async function definition after decorator [parse-error]
    --> sklearn/metrics/_classification.py:2884:1
     |
2884 | (y_true, y_pred, *, sample_weight=None, adjusted=False):
     | ^
     |
ERROR Parse error: Only single target (not tuple) can be annotated [parse-error]
    --> sklearn/metrics/_classification.py:2884:1
     |
2884 | (y_true, y_pred, *, sample_weight=None, adjusted=False):
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     |
ERROR Parse error: Expected an expression [parse-error]
    --> sklearn/metrics/_classification.py:2884:19
     |
2884 | (y_true, y_pred, *, sample_weight=None, adjusted=False):
     |                   ^
     |
ERROR Parse error: Expected `,`, found `=` [parse-error]
    --> sklearn/metrics/_classification.py:2884:34
     |
2884 | (y_true, y_pred, *, sample_weight=None, adjusted=False):
     |                                  ^
     |
ERROR Parse error: Expected `,`, found `=` [parse-error]
    --> sklearn/metrics/_classification.py:2884:49
     |
2884 | (y_true, y_pred, *, sample_weight=None, adjusted=False):
     |                                                 ^
     |
ERROR Parse error: Expected an expression [parse-error]
    --> sklearn/metrics/_classification.py:2884:57
     |
2884 | (y_true, y_pred, *, sample_weight=None, adjusted=False):
     |                                                         ^
2885 |     """Compute the balanced accuracy.
     |
ERROR Parse error: Unexpected indentation [parse-error]
    --> sklearn/metrics/_classification.py:2885:1
     |
2885 |     """Compute the balanced accuracy.
     | ^^^^
     |
ERROR Parse error: Expected an indented block after `if` statement [parse-error]
    --> sklearn/metrics/_classification.py:2972:5
     |
2972 |     n_classes = per_class.shape[0]
     |     ^^^^^^^^^
     |
ERROR Invalid `return` outside of a function [invalid-syntax]
    --> sklearn/metrics/_classification.py:2982:5
     |
2982 |     return float(score)
     |     ^^^^^^^^^^^^^^^^^^^
     |
ERROR Parse error: Expected a statement [parse-error]
    --> sklearn/metrics/_classification.py:2985:1
     |
2985 | @validate_params(
     | ^
     |
 INFO 10 errors (2 suppressed, 33 warnings not shown)