Use PDB to debug Python programs

 

This article discusses how to use PDB to debug Python without convenient ide tools. Program Source code example For example, there is a program to simulate tax calculation :#! /Usr/bin/Python Def debug_demo (VAL ): 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 __": The debug_demo (4500) debug_demo function calculates the taxes required for accounting for 4500. How to debug? 1. Add a breakpoint Add the red part to the place where the breakpoint needs to be inserted. Code : If the value of _ debug is true, debug is started here (the reason for adding _ debug is to enable/disable debugging conveniently ). #! /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. >/Usr/local/qspace/user_network/debug_demo.py (7) debug_demo () -> If Val <= 1600: (PDB)-> Val <= 1600: indicates the statement currently executed, (PDB) waiting for your debugging command. PDB provides a wide range of commands. You can enter the H command to view how to use the command. The following describes common commands: View the code context, L (lower case 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 10 Elif Val <= 3500: 11 print "Level 2" 12 print (Val-1600) * 0.05 (PDB) the row number on the left and the code body on the right. Monitoring variable: P variable name (PDB) P Val 4500 (PDB) One-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 10-> Elif Val <= 3500: 11 print "Level 2" 12 print (Val-1600) * 0.05 13 Elif Val <= 6500: 14 print "Level 3" 15 print (Val-3500) * 0.10 + (3500-1600) * 0.05 Add breakpoint: B row number (PDB) B 14 Run to breakpoint: c (PDB) c > /***** -> Print "Level 3" (PDB) L 9 print 0 10 Elif Val <= 3500: 11 print "Level 2" 12 print (Val-1600) * 0.05 13 Elif Val <= 6500: 14 B-> Print "Level 3" 15 print (Val-3500) * 0.10 + (3500-1600) * 0.05 16 else: 17 print "Level 4" 18 print (Val-6500) * 0.20 + (6500-3500) * 0.10 + (3500-1600) * 0.05 19 Before the function is returned: R (PDB) r Level 3 195.0 -- Return -- >/***** ()-> None -> Print (Val-3500) * 0.10 + (3500-1600) * 0.05 (PDB) Note: PDB also has many other useful commands that readers can explore on their own. Enter the H and H commands. You can get the Detailed Help of the command. However, I personally think that this debugging method does not need to be started. Generally, you can use log output for debugging unless you encounter a very subtle error. Then, the power of one-step debugging is displayed.

 

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