pdb

core code:

import pdb
pdb.set_trace()

pdb commands:

https://www.ibm.com/developerworks/cn/linux/l-cn-pythondebugger/index.html

you can get the value of code by  directly copy the code and enter!!!

offical document:

https://docs.python.org/2/library/pdb.html

https://docs.python.org/3/library/pdb.html