如何在python 2.7中回溯函数？

import inspect

def backtrace():
    for i, frame_info in enumerate(inspect.stack()):
        print("Frame {}:".format(i))
        print("  File: {}".format(frame_info[1]))
        print("  Line: {}".format(frame_info[2]))
        print("  Function: {}".format(frame_info[3]))
        print("  Code context:")
        for line in frame_info[4]:
            print("    {}".format(line.strip()))
        print("")

def foo():
    bar()

def bar():
    baz()

def baz():
    backtrace()

foo()

Frame 0:
  File: <ipython-input-1-000000000000>
  Line: 33
  Function:<module>
  Code context:
    backtrace()

Frame 1:
  File: <ipython-input-1-000000000000>
  Line: 28
  Function: baz
  Code context:
    print("  Code context:")
    for line in frame_info[4]:
    print("    {}".format(line.strip()))
    print("")

Frame 2:
  File: <ipython-input-1-000000000000>
  Line: 24
  Function: bar
  Code context:
    print("  Code context:")
    for line in frame_info[4]:
    print("    {}".format(line.strip()))
    print("")

Frame 3:
  File: <ipython-input-1-000000000000>
  Line: 20
  Function: foo
  Code context:
    print("  Code context:")
    for line in frame_info[4]:
    print("    {}".format(line.strip()))
    print("")