type_hints.py

import pandas as pd
from typing import Dict, List, Optional, Sequence, Tuple, Union

class DataProcessor:
    """Read and process data."""
    
    @classmethod
    def train_test_sets(
        cls,
        train_paths: Sequence[Union[Path, str]],
        test_paths: Optional[Sequence[Union[Path, str]]] = None,
        duplicate_threshold: int = 3,
    ) -> Tuple[pd.DataFrame, pd.DataFrame]:
        """Create train and test Pandas DataFrames while avoiding leakage-flow in train/test."""
        train_df: pd.DataFrame = DataProcessor.concatenate_datasets(train_paths)
            
        test_df: Optional[pd.DataFrame] = None
        if test_paths:
            test_df = DataProcessor.concatenate_datasets(test_paths)
        
        return train_df, test_df