In Java/C# you can easily step through code to trace what might be going wrong, and IDE's make this process very user friendly.
Can you trace through python code in a similar fashion?
Yes! There's a Python debugger called
pdb just for doing that!
You can launch a Python program through
pdb by using
pdb myscript.py or
python -m pdb myscript.py.
There are a few commands you can then issue, which are documented on the
Some useful ones to remember are:
b: set a breakpoint
c: continue debugging until you hit a breakpoint
s: step through the code
n: to go to next line of code
l: list source code for the current file (default: 11 lines including the line being executed)
u: navigate up a stack frame
d: navigate down a stack frame
p: to print the value of an expression in the current context
If you don't want to use a command line debugger, some IDEs like Pydev, Wing IDE or PyCharm have a GUI debugger. Wing and PyCharm are commercial products, but Wing has a free "Personal" edition, and PyCharm has a free community edition.
First step is to make the Python interpreter to enter into the debugging mode.
A. From the Command Line
Most straight forward way, running from command line, of python interpreter
$ python -m pdb scriptName.py > .../pdb_script.py(7)<module>() -> """ (Pdb)
B. Within the Interpreter
While developing early versions of modules and to experiment it more iteratively.
$ python Python 2.7 (r27:82508, Jul 3 2010, 21:12:11) [GCC 4.0.1 (Apple Inc. build 5493)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import pdb_script >>> import pdb >>> pdb.run('pdb_script.MyObj(5).go()') > <string>(1)<module>() (Pdb)
C. From Within Your Program
For a big project and long-running module, can start the debugging from inside the program using import pdb and set_trace() like this :
#!/usr/bin/env python # encoding: utf-8 # import pdb class MyObj(object): count = 5 def __init__(self): self.count= 9 def go(self): for i in range(self.count): pdb.set_trace() print i return if __name__ == '__main__': MyObj(5).go()
Step-by-Step debugging to go into more internal
Execute the next statement… with “n” (next)
Repeating the last debugging command… with ENTER
Quitting it all… with “q” (quit)
Printing the value of variables… with “p” (print)
a) p a
Turning off the (Pdb) prompt… with “c” (continue)
Seeing where you are… with “l” (list)
Stepping into subroutines… with “s” (step into)
Continuing… but just to the end of the current subroutine… with “r” (return)
Assign a new value
a) !b = "B"
Set a breakpoint
a) break linenumber
b) break functionname
c) break filename:linenumber
a) tbreak linenumber
a) break linenumber, condition
Note:**All these commands should be execute from **pdb
For in-depth knowledge, refer:-