How to use the numexpr.necompiler.getExprNames function in numexpr

strexpr = strexpr[0]

    # Get the variable names used in the condition.
    # At the same time, build its signature.
    varnames = _get_variable_names(expr)
    signature = [(var, typemap[var]) for var in varnames]
    try:
        # See the comments in `numexpr.evaluate()` for the
        # reasons of inserting copy operators for unaligned,
        # *unidimensional* arrays.
        func = NumExpr(expr, signature)
    except NotImplementedError as nie:
        # Try to make this Numexpr error less cryptic.
        raise _unsupported_operation_error(nie)

    _, ex_uses_vml = getExprNames(condition, {})
    kwargs = {'ex_uses_vml': ex_uses_vml}

    params = varnames
    # This is more comfortable to handle about than a tuple.
    return CompiledCondition(func, params, idxexprs, strexpr, **kwargs)

def get_cnames(expr,
               _names_cache=ne.utils.CacheDict(256) if ne else ne,
               _numexpr_cache=ne.utils.CacheDict(256) if ne else ne, 
               **kwargs):
    if not isinstance(expr, (str, unicode)):
        raise ValueError("must specify expression as a string")
    # Get the names for this expression
    context = ne.necompiler.getContext(kwargs, frame_depth=1)
    expr_key = (expr, tuple(sorted(context.items())))
    if expr_key not in _names_cache:
        _names_cache[expr_key] = ne.necompiler.getExprNames(expr.strip(),
                                                            context)
    names, ex_uses_vml = _names_cache[expr_key]
    return names

def get_cnames(expr,
               _names_cache=ne.utils.CacheDict(256) if ne else ne,
               _numexpr_cache=ne.utils.CacheDict(256) if ne else ne,
               **kwargs):
    if not isinstance(expr, (str, unicode)):
        raise ValueError("must specify expression as a string")
    # Get the names for this expression
    context = ne.necompiler.getContext(kwargs, frame_depth=1)
    expr_key = (expr, tuple(sorted(context.items())))
    if expr_key not in _names_cache:
        _names_cache[expr_key] = ne.necompiler.getExprNames(expr.strip(),
                                                            context)
    names, ex_uses_vml = _names_cache[expr_key]
    return names

self.stop = None
        """The stop range selection for the input."""
        self.step = None
        """The step range selection for the input."""
        self.values = []
        """The values of variables in expression (list)."""

        self._compiled_expr = None
        """The compiled expression."""
        self._single_row_out = None
        """A sample of the output with just a single row."""

        # First, get the signature for the arrays in expression
        vars_ = self._required_expr_vars(expr, uservars)
        context = getContext(kwargs)
        self.names, _ = getExprNames(expr, context)

        # Raise a ValueError in case we have unsupported objects
        for name, var in vars_.items():
            if type(var) in (int, float, str):
                continue
            if not isinstance(var, (tb.Leaf, tb.Column)):
                if hasattr(var, "dtype"):
                    # Quacks like a NumPy object
                    continue
                raise TypeError("Unsupported variable type: %r" % var)
            objname = var.__class__.__name__
            if objname not in ("Array", "CArray", "EArray", "Column"):
                raise TypeError("Unsupported variable type: %r" % var)

        # NumPy arrays to be copied? (we don't need to worry about
        # PyTables objects, as the reads always return contiguous and

def _validate(self):
        """
        Ensure that our expression string has variables of the form x_0, x_1,
        ... x_(N - 1), where N is the length of our inputs.
        """
        variable_names, _unused = getExprNames(self._expr, {})
        expr_indices = []
        for name in variable_names:
            if name == 'inf':
                continue
            match = _VARIABLE_NAME_RE.match(name)
            if not match:
                raise ValueError("%r is not a valid variable name" % name)
            expr_indices.append(int(match.group(2)))

        expr_indices.sort()
        expected_indices = list(range(len(self.inputs)))
        if expr_indices != expected_indices:
            raise ValueError(
                "Expected %s for variable indices, but got %s" % (
                    expected_indices, expr_indices,
                )

def evaluate(tree, expression):
    cleaned_expression, alias_dict = preprocess_expression(expression)
    context = numexpr.necompiler.getContext({}, frame_depth=1)
    variables = numexpr.necompiler.getExprNames(cleaned_expression, context)[0]
    try:
        adaptor = TreeToDictAdaptor(tree, alias_dict, variables)
    except ValueError:
        msg = "Cannot broadcast all variables in expression: %s" % expression
        logger.error(msg)
        raise ValueError(msg)
    result = numexpr.evaluate(cleaned_expression, local_dict=adaptor)
    result = adaptor.apply_jaggedness(result)
    return result