"""Create fallback_executor
Generated by Phi-Octopus Eden
2025-11-08 14:17:31.125173
"""

```python
from typing import Callable, Optional


class FallbackExecutor:
    """
    A class that provides a mechanism for executing tasks with fallback options in case of errors.

    Attributes:
        primary_executer (Callable): The main function to be executed.
        fallback_executor (Optional[Callable]): An alternative function to execute if the primary fails.
    """

    def __init__(self, primary_executer: Callable, fallback_executor: Optional[Callable] = None):
        """
        Initialize FallbackExecutor with a primary and an optional fallback executor.

        Args:
            primary_executer (Callable): The main function to be executed.
            fallback_executor (Optional[Callable]): An alternative function to execute if the primary fails. Default is None.
        """
        self.primary_executer = primary_executer
        self.fallback_executor = fallback_executor

    def execute(self, *args, **kwargs) -> Optional[str]:
        """
        Execute the primary executor and handle errors by falling back on another function.

        Args:
            *args: Variable length argument list to pass to the executers.
            **kwargs: Arbitrary keyword arguments to pass to the executers.

        Returns:
            Optional[str]: The result of the execution or None if both fail. Error message is returned as str.
        """
        try:
            return self.primary_executer(*args, **kwargs)
        except Exception as e:
            if self.fallback_executor:
                try:
                    return self.fallback_executor(*args, **kwargs)
                except Exception as f_e:
                    return f"Primary and fallback executors failed: {str(e)}, {str(f_e)}"
            else:
                return str(e)


# Example usage
def primary_add(a: int, b: int) -> int:
    """Add two numbers."""
    return a + b


def fallback_subtract(a: int, b: int) -> int:
    """Subtract one number from another as an alternative operation."""
    return a - b


executor = FallbackExecutor(primary_executer=primary_add, fallback_executor=fallback_subtract)

print(executor.execute(10, 5))  # Should print 15
print(executor.execute(10, 20))  # Should raise an error and fallback to subtraction

# Expected output:
# 15
# 10 - 20 = -10
```