[Go] How to debug a python program

Debugging method of qi09 original Python program

This article discusses using the PDB to debug a python program when no convenient IDE tool is available

Source code Example

For example, there are procedures for simulating tax calculations:

#!/usr/bin/pythondefDebug_demo (val):ifVal <= 1600 :                                 Print "Level 1"                                 Print0elifVal <= 3500 :                                 Print "Level 2"                                 Print(val-1600) * 0.05elifVal <= 6500 :                                 Print "Level 3"                                 Print(val-3500) * 0.10 + (3500-1600) * 0.05Else:                                 Print "Level 4"                                 Print(val-6500) * 0.20 + (6500-3500) * 0.10 + (3500-1600) * 0.05#~def Debug_demoif __name__=="__main__": Debug_demo (4500)

The Debug_demo function calculates the tax required for 4500 of the recorded entries.

How to debug?

1. Adding Breakpoints

Add a red part of the code where you want to insert a breakpoint: If the _DEBUG value is true, start debugging at that point (the reason for joining _DEBUG is to facilitate debugging on/off).

#!/usr/bin/python
_debug=true
Def Debug_demo (val):
if _debug = = True:
Import PDB
Pdb.set_trace ()
If Val <= 1600:
Print "Level 1"
Print 0
Elif Val <= 3500:
Print "Level 2"
Print (val-1600) * 0.05
Elif Val <= 6500:
Print "Level 3"
Print (val-3500) * 0.10 + (3500-1600) * 0.05
Else
Print "Level 4"
Print (val-6500) * 0.20 + (6500-3500) * 0.10 + (3500-1600) * 0.05
#~def Debug_demo
if __name__ = = "__main__":
Debug_demo (4500)

2. Start Running debugging

Run the program./debug_demo.py, get

>/usr/local/qspace/user_network/debug_demo.py (7) Debug_demo ()
If Val <= 1600:
(PDB)

Val <= 1600: Indicates the currently executing statement, (PDB) waits for your debug instruction. The PDB commands are rich, and the input h instruction allows you to see how the instructions are used.

The following is a brief introduction to common directives:

View Code context, L (lowercase l)

(PDB) L
2 _debug=true
3 def Debug_demo (val):
4 if _debug = = True:
5 Import PDB
6 Pdb.set_trace ()
7-If Val <= 1600:
8 print "Level 1"
9 Print 0
Ten elif val <= 3500:
Print "Level 2"
Print (val-1600) * 0.05
(PDB)

The left is the line number and the right is the code body.

monitor variable: P variable name

(PDB) P Val
4500
(PDB)

Single Step execution: N

-Elif Val <= 3500:
(PDB) L
5 Import PDB
6 Pdb.set_trace ()
7 if Val <= 1600:
8 print "Level 1"
9 Print 0
Elif Val <= 3500:
Print "Level 2"
Print (val-1600) * 0.05
Elif Val <= 6500:
Print "Level 3"
Print (val-3500) * 0.10 + (3500-1600) * 0.05

Add Breakpoint: B line number

(Pdb) b 14

Run to breakpoint: C

(PDB) C
>/*****
Print "Level 3"
(PDB) L
9 Print 0
Ten elif val <= 3500:
Print "Level 2"
Print (val-1600) * 0.05
Elif Val <= 6500:
b-> print "Level 3"
Print (val-3500) * 0.10 + (3500-1600) * 0.05
+ Else:
Print "Level 4"
Print (val-6500) * 0.20 + (6500-3500) * 0.10 + (3500-1600) * 0.05
19

before executing to function return: R

(PDB) R
Level 3
195.0
--return--
>/**** ()

->none
Print (val-3500) * 0.10 + (3500-1600) * 0.05
(PDB)

Description:

The PDB also has many other useful instructions that readers can explore on their own. Enter the H,h command. You can get the detailed help of the command.

However, I personally think that generally do not need to start this debugging method, generally use the log output for debugging, unless you encounter a very subtle error. At this point, the power of one-step debugging is displayed.

[goto] Python program debugging methods