TypeVar bound - restricting the type range

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The 'bound' argument to TypeVar sets an upper bound: T can only be substituted with the bound type or one of its subclasses. With bound=int, passing a plain int is fine, and passing a bool works too because bool is a subclass of int in Python. Passing float would fail static analysis because float does not inherit from int. This is different from constraining T to specific types like TypeVar('T', int, str), which means T must be exactly int or exactly str - no subclasses allowed for constrained TypeVars. Bounded TypeVars appear frequently in numeric code where you want a generic that works on int and its subtypes but you rely on integer arithmetic being available.