Python debugging: logging and pdb (example analysis 2)

In the previous article, we learned why python needs to be debugged, and introduced two methods of python debugging. However, the debugging method cannot be explained in one article, so in this article we will talk about it. Let’s look at the remaining two debugging methods. I hope these debugging methods can be helpful to you and help you move forward more quickly on the road to learning python.

logging

The third method is to replace print() with logging. Compared with assert, logging will not throw an error, and It can be output to a file:

import logging
s = '0'
n = int(s)
logging.info('n = %d' % n)
print(10 / n)

logging.info() can output a piece of text. Run and find no information except ZeroDivisionError. what happened?

Don’t worry, add a line of configuration after import logging and try again:

import logging
logging.basicConfig(level=logging.INFO)

See the output:

$ python err.py
INFO:root:n = 0
Traceback (most recent call last):
  File "err.py", line 8, in <module>
    print(10 / n)
ZeroDivisionError: division by zero

This is the benefit of logging, it allows you to specify records The levels of information include debug, info, warning, error, etc. When we specify level=INFO, logging.debug will not work. In the same way, after specifying level=WARNING, debug and info will not work. In this way, you can safely output different levels of information without deleting it, and finally control which level of information is output.

Another benefit of logging is that through simple configuration, a statement can be output to different places at the same time, such as the console and files.

pdb

The fourth way is to start the Python debugger pdb, let the program run in single-step mode, and you can check the running status at any time . We first prepare the program

# err.py
s = '0'
n = int(s)
print(10 / n)

and then start it:

$ python -m pdb err.py
> /Users/michael/Github/learn-python3/samples/debug/err.py(2)<module>()
-> s = &#39;0&#39;

After starting with the parameter -m pdb, pdb locates the code to be executed next -> s = '0' . Enter the command l to view the code:

 (Pdb) l
  1     # err.py
  2  -> s = '0'
  3     n = int(s)
  4     print(10 / n)

Enter the command n to step through the code:

(Pdb) n
> /Users/michael/Github/learn-python3/samples/debug/err.py(3)<module>()
-> n = int(s)
(Pdb) n
> /Users/michael/Github/learn-python3/samples/debug/err.py(4)<module>()
-> print(10 / n)

You can enter the command p variable name at any time to view the variable:

(Pdb) p s
'0'
(Pdb) p n
0

Enter the command q to end debugging and exit the program:

(Pdb) q

(This method of debugging on the command line through pdb is theoretically omnipotent, but it is really too troublesome)

That’s it for this article For all the content described in the article, this article mainly introduces the relevant knowledge of python debugging. I hope you can use the information to understand the above content. I hope what I have described in this article will be helpful to you and make it easier for you to learn python.

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