Class PossiblyUndefinedVariableVisitor

mypy/partially_defined.py:304–703

Detects the following cases: - A variable that's defined only part of the time. - If a variable is used before definition An example of a partial definition: if foo(): x = 1 print(x) # Error: "x" may be undefined. Example of a used before definition: x = y

class PossiblyUndefinedVariableVisitor(ExtendedTraverserVisitor):
    """Detects the following cases:
    - A variable that's defined only part of the time.
    - If a variable is used before definition

    An example of a partial definition:
    if foo():
        x = 1
    print(x)  # Error: "x" may be undefined.

    Example of a used before definition:
    x = y
    y: int = 2

    Note that this code does not detect variables not defined in any of the branches -- that is
    handled by the semantic analyzer.
    """

    def __init__(
        self,
        msg: MessageBuilder,
        type_map: dict[Expression, Type],
        options: Options,
        names: SymbolTable,
    ) -> None:
        self.msg = msg
        self.type_map = type_map
        self.options = options
        self.builtins = SymbolTable()
        builtins_mod = names.get("__builtins__", None)
        if builtins_mod:
            assert isinstance(builtins_mod.node, MypyFile)
            self.builtins = builtins_mod.node.names
        self.loops: list[Loop] = []
        self.try_depth = 0
        self.tracker = DefinedVariableTracker()
        for name in implicit_module_attrs:
            self.tracker.record_definition(name)

    def var_used_before_def(self, name: str, context: Context) -> None:
        if self.msg.errors.is_error_code_enabled(errorcodes.USED_BEFORE_DEF):
            self.msg.var_used_before_def(name, context)

    def variable_may_be_undefined(self, name: str, context: Context) -> None:
        if self.msg.errors.is_error_code_enabled(errorcodes.POSSIBLY_UNDEFINED):
            self.msg.variable_may_be_undefined(name, context)

    def process_definition(self, name: str) -> None:
        # Was this name previously used? If yes, it's a used-before-definition error.
        if not self.tracker.in_scope(ScopeType.Class):
            refs = self.tracker.pop_undefined_ref(name)
            for ref in refs:
                if self.loops:
                    self.variable_may_be_undefined(name, ref)
                else:
                    self.var_used_before_def(name, ref)
        else:
            # Errors in class scopes are caught by the semantic analyzer.