Python Type Checking with MyPy

Python is dynamically typed, so many type errors appear only when code runs.

        MyPy helps by checking types before execution.
        This is especially helpful in:
        - large projects
        - team projects
        - long-term maintainable code
        
        ## Install MyPy
        
        ```bash
        pip install mypy
        ```
        
        ## Simple example (type error is caught early)
        
        ```python
        def add(a: int, b: int) -> int:
            return a + b
        
        result = add("5", "3")  # wrong types
        ```
        
        Run:
        ```bash
        mypy code.py
        ```
        
        ## Optional types (None handling)
        
        ```python
        from typing import Optional
        
        def find_user(user_id: int) -> Optional[str]:
            if user_id == 1:
                return "Tom"
            return None
        
        user = find_user(2)
        if user is not None:
            print(user.upper())
        ```
        
        ## Collections types
        
        ```python
        from typing import List, Dict, Tuple, Set
        
        names: List[str] = ["Tom", "Sarah"]
        scores: Dict[str, int] = {"Tom": 90}
        point: Tuple[int, int] = (10, 20)
        unique: Set[int] = {1, 2, 3}
        ```
        
        ## Generics example (Stack)
        
        ```python
        from typing import TypeVar, Generic, List
        
        T = TypeVar("T")
        
        class Stack(Generic[T]):
            def __init__(self) -> None:
                self.items: List[T] = []
        
            def push(self, item: T) -> None:
                self.items.append(item)
        
            def pop(self) -> T:
                return self.items.pop()
        
        s = Stack[int]()
        s.push(10)
        ```
        
        ## Graph: bug prevention
        
        ```mermaid
        flowchart LR
          A[Write code] --> B[Run mypy]
          B --> C{Types OK?}
          C -->|Yes| D[Run program safely]
          C -->|No| E[Fix type errors early]
        ```
        
        ## Remember
        
        - Type hints improve readability
        - MyPy catches many bugs before runtime
        - Best for medium/large codebases