How to use the datatable.expr.expr.Expr function in datatable

def cov(expr1, expr2):
    return Expr(OpCodes.COV, (expr1, expr2))

def __sub__(self, other):
        return Expr(OpCodes.MINUS, (self, other))

def sd(expr):
    return Expr(OpCodes.STDEV, (expr,))

def count(iterable=None):
    if isinstance(iterable, Expr):
        return Expr(OpCodes.COUNT, (iterable,))
    elif iterable is None:
        return Expr(OpCodes.COUNT0, ())
    else:
        return _builtin_sum((x is not None) for x in iterable)

def __rshift__(self, other):
        return Expr(OpCodes.RSHIFT, (self, other))

def __gt__(self, other):
        return Expr(OpCodes.GT, (self, other))

def remove(self, other):
        return Expr(OpCodes.SETMINUS, (self, other))

def __ge__(self, other):
        return Expr(OpCodes.GE, (self, other))

def last(iterable):
    if isinstance(iterable, Expr):
        return Expr(OpCodes.LAST, (iterable,))
    else:
        try:
            for x in reversed(iterable):
                return x
        except TypeError:
            # Some iterators may not be reversible
            x = None
            for x in iterable:
                pass
            return x

def __floordiv__(self, other):
        return Expr(OpCodes.INTDIV, (self, other))