<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def make_symbolic(self, name, addr, length=None):
 """ Replaces `length` bytes starting at `addr` with a symbolic variable named name. Adds a constraint equaling that symbolic variable to the value previously at `addr`, and returns the variable. """

        l.debug("making %s bytes symbolic", length)

        if isinstance(addr, str):
            addr, length = self.state.arch.registers[addr]
        else:
            if length is None:
                raise Exception("Unspecified length!")

        r = self.load(addr, length)

        v = self.get_unconstrained_bytes(name, r.size())
        self.store(addr, v)
        self.state.add_constraints(r == v)
        l.debug("... eq constraints: %s", r == v)
        return v