Method _required_expr_vars

tables/expression.py:247–331

Get the variables required by the `expression`. A new dictionary defining the variables used in the `expression` is returned. Required variables are first looked up in the `uservars` mapping, then in the set of top-level columns of the table. Unknown variables caus

(
        self,
        expression: str,
        uservars: dict[str, Any] | None,
        depth: int = 2,
    )

    # The next method is similar to their counterpart in `Table`, but
    # adapted to the `Expr` own requirements.
    def _required_expr_vars(
        self,
        expression: str,
        uservars: dict[str, Any] | None,
        depth: int = 2,
    ) -> dict[str, Any]:
        """Get the variables required by the `expression`.

        A new dictionary defining the variables used in the `expression`
        is returned.  Required variables are first looked up in the
        `uservars` mapping, then in the set of top-level columns of the
        table.  Unknown variables cause a `NameError` to be raised.

        When `uservars` is `None`, the local and global namespace where
        the API callable which uses this method is called is sought
        instead.  To disable this mechanism, just specify a mapping as
        `uservars`.

        Nested columns and variables with an ``uint64`` type are not
        allowed (`TypeError` and `NotImplementedError` are raised,
        respectively).

        `depth` specifies the depth of the frame in order to reach local
        or global variables.

        """
        # Get the names of variables used in the expression.
        exprvars_cache = self._exprvars_cache
        if expression not in exprvars_cache:
            # Protection against growing the cache too much
            if len(exprvars_cache) > 256:
                # Remove 10 (arbitrary) elements from the cache
                for k in list(exprvars_cache)[:10]:
                    del exprvars_cache[k]
            cexpr = compile(expression, "<string>", "eval")
            exprvars = [
                var
                for var in cexpr.co_names
                if var not in ["None", "False", "True"]
                and var not in ne.expressions.functions
            ]
            exprvars_cache[expression] = exprvars
        else:
            exprvars = exprvars_cache[expression]

        # Get the local and global variable mappings of the user frame
        # if no mapping has been explicitly given for user variables.
        user_locals, user_globals = {}, {}
        if uservars is None:
            user_frame = sys._getframe(depth)
            user_locals = user_frame.f_locals
            user_globals = user_frame.f_globals

        # Look for the required variables first among the ones
        # explicitly provided by the user.
        reqvars = {}
        for var in exprvars:
            # Get the value.