How to Debug Python Code in Terminal
When I use Pycharm a while ago,
I get used to debugging my code with its built-in GUI debugger, which works
really well. But when I write code on a server without X11 support, I am forced
to use Neovim for Python development. My debugging is
reduced to a serize of
Finally, I decided to give terminal debuggers a try. In this post, I introduce three debuggers.
Python ships with a native debugger called pdb.
You can debug your code with intrusive way or non-introsive way. For the intrusive way, you need to modify your source code:
import pdb # put the following statement where you want the code to stop and step to pdb pdb.set_trace()
Personally, I prefer the non-intrusive way to invode pdb. You can run pdb as module:
python -m pdb your_script.py
It will start debugging your code from the begining of the code.
Pdb provides a few commands to help you debug your code on its interacitve interface. Here, I list some of the commands and their meanings:
n: execute the next line
p: print the value of an object
s: step into a function
r: return from a function
b [num]: set a breakpoint at line
c: continue to run the code until a break point is met
unt [NUM]: run the code until line
whatis: print the type of object (similar to
l: list the context of current line (default 11 lines)
h: show help message
q: quit the debugger
How to enable autocomplete
By default, pdb does not provide auto-completion for variable names and object
methods. To enable auto-completion, create a file
.pdbrc under your HOME
directory with the following settings:
import rlcompleter import pdb pdb.Pdb.complete=rlcompleter.Completer(locals()).complete
Ipdb is like pdb, but with built-in autocompletion, syntax highlighting and more commands. You can install it with pip:
pip install ipdb
Its usage is similar to pdb, so I will not waste time here. One thing worth
noting is that ipdb adds a
sticky [start end] Toggle sticky mode. When in sticky mode, it clear the screen and longlist the current functions, making the source appearing always in the same position. Useful to follow the flow control of a function when doing step-by-step execution. If ``start`` and ``end`` are given, sticky mode is enabled and only lines within that range (extremes included) will be displayed.
It means that in stick mode, the current function will be shown and current line will be highlighted to make your follow the execution of program easier.
Another terminal debugger worth trying is pudb. First, install it with pip:
pip install pudb
To invoke it, you can either use
python -m pudb my_script.py
Pudb creates a GUI-like interface for debugging your code. It will show your code, current variable, stack trace, break points and a terminal window in its terminal interface.
You can use
j to move the cursor line up and down and use
b to set
a break point, which will be highlighted in red. To execute next line of code,
n. To run the code until a break point, use
c. For more usage, press
Overall, it is quite powerful, considering that it is implemented in a terminal.
In this post, I introduced three Python debuggers — pdb, ipdb and pudb. They can both help us to debug the code. Personally, I think pudb is the most beautiful one I want to use.
Title image is taken from here
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