Debugging in Spyder is supported thanks to the following Python modules:
- pdb: the Python debugger, which is included in Python standard library
- winpdb: a graphical frontend to pdb, which is an external package (in the Editor, press F7 to run winpdb on the currently edited script)
The Python debugger is partly integrated in Spyder:
- simple breakpoints and conditonal breakpoints may be defined in the Editor
- the current frame (debugging step) is highlighted in the Editor
- at each breakpoint, globals may be accessed through the Variable Explorer
For a simple, yet quite complete introduction to pdb, you may read this: http://pythonconquerstheuniverse.wordpress.com/category/python-debugger/