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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def solve_step(self):
 """Perform a single solve step. """

        self.solve_begun = True
        if self.status != SolverStatus.unsolved:
            return

        if self.pr:
            self.pr.header("SOLVE #%d (%d fails so far)...",
                           self.solve_count + 1, self.num_fails)

        phase = self._pop_phase()

        if phase.status == SolverStatus.failed:  # a previously failed phase
            self.pr("discarded failed phase, fetching previous unsolved phase...")
            self.failed_phase_list.append(phase)
            phase = self._pop_phase()

        if phase.status == SolverStatus.exhausted:
            self.pr.subheader("SPLITTING:")
            phase, next_phase = phase.split()
            self._push_phase(next_phase)
            if self.pr:
                self.pr("new phase: %s", phase)

        new_phase = phase.solve()
        self.solve_count += 1

        if new_phase.status == SolverStatus.failed:
            self.pr.subheader("FAILED:")
            self._push_phase(new_phase)
            if self.pr and len(self.phase_stack) == 1:
                self.pr.header("FAIL: there is no solution")

        elif new_phase.status == SolverStatus.solved:
            # solved, but there may be cyclic dependencies
            self.pr.subheader("SOLVED:")
            final_phase = new_phase.finalise()
            self._push_phase(final_phase)

            if self.pr:
                if final_phase.status == SolverStatus.cyclic:
                    self.pr.header("FAIL: a cycle was detected")
                else:
                    self.pr.header("SUCCESS")

        else:
            self.pr.subheader("EXHAUSTED:")
            assert(new_phase.status == SolverStatus.exhausted)
            self._push_phase(new_phase)