You can use the pdb module, insert pdb.set_trace() anywhere and it will function as a breakpoint.
>>> import pdb
>>> a="a string"
(Pdb) p a
To continue execution use c (or cont or continue).
It is possible to execute arbitrary Python expressions using pdb. For example, if you find a mistake, you can correct the code, then type a type expression to have the same effect in the running code
ipdb is a version of pdb for IPython. It allows the use of pdb with all the IPython features including tab completion.
It is also possible to set pdb to automatically run on an uncaught exception.