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Testing & modern typing

pytest basics, mocks, type hints, TypedDict, Protocol, and static-checking patterns.

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How to Validate Data in Python with Typing Hints

Build a runtime validation helper that checks values against Python type hints like Optional, list, and basic types.

typing validation type-hints
Python 
from typing import Any, Optional, Union, TypeVar, get_origin, get_args

T = TypeVar("T")

def validate(value: Any, expected_type: type) -> Optional[str]:
    """Returns an error message if value doesn't match expected_type, else None."""
    # Handle Optional[...] types
    origin = get_origin(expected_type)
    if or…
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