Debugging in Python
A guide to knowing and implementing the Python debugger module.
3 min readOct 22, 2020
The Python module used to debug the code is called as “pdb”. It provides an interactive debugging program for Python programs. It has features that allow you to pause the program, check the values of different variables and watch the step-by-step execution of the program. This helps in finding bugs in the logic.
Let’s consider a code with an error to see how this works.
>>> import pdb>>> a = [11,44,77]
>>> b = 1
>>> c = 9>>> result = b + c
>>> print(result)# wrong line of code
>>> result2 = a + b
>>> print(result2)10
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-2-29b30ba110f3> in <module>
7
8 # wrong line of code
----> 9 result2 = a + b
10 print(result2)TypeError: can only concatenate list (not "int") to list
So as you can see there is an error because a list and integer cannot be added. Now we will set a trace using the module. So go to the line where there is an error and trace it. When this code is run, the interactive debugging environment is shown. Press ‘q’ to quit the debugging environment.
>>> a = [11,44,77]
>>> b = 1
>>> c = 9>>> result = b + c
>>> print(result)>>> pdb.set_trace()# wrong line of code
>>> result2 = a + b
>>> print(result2)10
--Return--
None
> <ipython-input-3-c41ee9df98d8>(8)<module>()
6 print(result)
7
----> 8 pdb.set_trace()
9
10 # wrong line of codeipdb> q
---------------------------------------------------------------------------
BdbQuit Traceback (most recent call last)
<ipython-input-3-c41ee9df98d8> in <module>
6 print(result)
7
----> 8 pdb.set_trace()
9
10 # wrong line of codeD:\Anaconda3\lib\bdb.py in trace_dispatch(self, frame, event, arg)
90 return self.dispatch_call(frame, arg)
91 if event == 'return':
---> 92 return self.dispatch_return(frame, arg)
93 if event == 'exception':
94 return self.dispatch_exception(frame, arg)D:\Anaconda3\lib\bdb.py in dispatch_return(self, frame, arg)
152 finally:
153 self.frame_returning = None
--> 154 if self.quitting: raise BdbQuit
155 # The user issued a 'next' or 'until' command.
156 if self.stopframe is frame and self.stoplineno != -1:BdbQuit:
Refer to the notebook here.
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