Python Debugger
The Python module pdb defines an interactive source code debugger for Python programs. It supports the following features:
- setting breakpoints,
- single stepping at the source code line level,
- inspection of stack frames,
- source code listing, and
- evaluation of arbitrary Python code in the context of any stack frame.
You can use the pdb module to run your Python script interactive mode for debugging purpose, for example:
$ python3 -m pdb a1_template.py
>/home/rchan/ops435/a1/a1_template.py(2)<module>()
-> '''template for ops435 assignment 1 script
(Pdb)Contents
Debugger Commands
Now you are in the Python debugging mode with the Python script "a1_template.py" loaded. The (Pdb) prompt shown at the beginning of the line indicates that the Python interpreter is running under the debugging mode. You can type the word "help" without open or close bracket to get a list of debugging commands:
(Pdb) help
(Pdb) help
Documented commands (type help <topic>):
<source>
========================================
EOF c d h list q rv undisplay
a cl debug help ll quit s unt
alias clear disable ignore longlist r source until
args commands display interact n restart step up
b condition down j next return tbreak w
break cont enable jump p retval u whatis
bt continue exit l pp run unalias where
Miscellaneous help topics:
==========================
exec pdb
(Pdb)Online help on Debugger commands
There are quite a bit of commands to get familiar with. However, we only need to learn a few to get started. Here are the ones that you should know: l, ll, n, s, and b
(Pdb) help l
l(ist) [first [,last] | .]
List source code for the current file. Without arguments,
list 11 lines around the current line or continue the previous
listing. With . as argument, list 11 lines around the current
line. With one argument, list 11 lines starting at that line.
With two arguments, list the given range; if the second
argument is less than the first, it is a count.
The current line in the current frame is indicated by "->".
If an exception is being debugged, the line where the
exception was originally raised or propagated is indicated by
">>", if it differs from the current line.
(Pdb) help ll
longlist | ll
List the whole source code for the current function or frame.
(Pdb) help n
n(ext)
Continue execution until the next line in the current function
is reached or it returns.
(Pdb) help s
s(tep)
Execute the current line, stop at the first possible occasion
(either in a function that is called or in the current
function).
(Pdb) help b
b(reak) [ ([filename:]lineno | function) [, condition] ]
Without argument, list all breaks.
With a line number argument, set a break at this line in the
current file. With a function name, set a break at the first
executable line of that function. If a second argument is
present, it is a string specifying an expression which must
evaluate to true before the breakpoint is honored.
The line number may be prefixed with a filename and a colon,
to specify a breakpoint in another file (probably one that
hasn't been loaded yet). The file is searched for on
sys.path; the .py suffix may be omitted.
(Pdb)Try it out: l, ll, b, n, s
The list command: l or list
We will first use 'l' to list Python code around the current Python statement to be executed:
(Pdb) l
1 #!/usr/bin/env python3
2 -> ''' template for ops435 assignment 1 script
3 put your script level docstring here...
4 you can have more than one line of docstring.
5 Please personlize the following author declaration:
6 -----------------------------------------------------------------------
7 OPS435 Assignment 1 - Fall 2020
8 Program: a1_[Seneca_name].py (replace [Seneca_name] with your Seneca User name)
9 Author: "Student Name"
10 The python code in this file (a1_[Seneca_name].py) is original work written by
11 "Student Name". No code in this file is copied from any other sourcethe longlist command: ll or longlist
We can list all the Python statements in the current file with 'll' or 'longlist' command:
(Pdb) ll
1 #!/usr/bin/env python3
2 -> ''' template for ops435 assignment 1 script
3 put your script level docstring here...
4 you can have more than one line of docstring.
5 Please personlize the following author declaration:
6 -----------------------------------------------------------------------
7 OPS435 Assignment 1 - Fall 2020
8 Program: a1_[Seneca_name].py (replace [Seneca_name] with your Seneca User name)
9 Author: "Student Name"
10 The python code in this file (a1_[Seneca_name].py) is original work written by
11 "Student Name". No code in this file is copied from any other source
12 except those provided by the course instructor, including any person,
13 textbook, or on-line resource. I have not shared this python script
14 with anyone or anything except for submission for grading.
15 I understand that the Academic Honesty Policy will be enforced and
16 violators will be reported and appropriate action will be taken.
17 '''
18 import os
19 import sys
20
21 def leap_year(obj):
22 '''
23 put your function level docstring here ...
24 '''
25 ...
26
27 return status
28
29 def sanitize(obj1,obj2):
30 '''
31 put your function level docstring here ...
32 '''
33 ...
34
35 return results
36
37 def size_check(obj, intobj):
38 '''
39 put your function level docstring here ..
40 '''
41 ...
42
43 return status
44
45 def range_check(obj1, obj2):
46 '''
47 put your function level docstring here ..
48 '''
49 ...
50
51 return status
52
53 def usage():
54 '''
55 put your function level docstring here ...
56 '''
57 ...
58 return status
59
60 if __name__ == "__main__":
61 # step 1
62 if len(sys.argv) != 2:
63 print(usage())
64 sys.exit()
65 # step 2
66 B month_name = ['Jan','Feb','Mar','Apr','May','Jun',
67 'Jul','Aug','Sep','Oct','Nov','Dec']
68 days_in_month = {1:31, 2:28, 3:31, 4:30, 5:31, 6:30,
69 7:31, 8:31, 9:30, 10:31, 11:30, 12:31}
70 user_raw_data = sys.argv[1]
71 # step 3
72 allow_chars = '0123456789'
73 dob = sanitize(user_raw_data, allow_chars)
74 print('Sanitized user data:', dob)
75 # setp 4
76 result = size_check(dob,8)
77 if result == False:
78 print("Error 09: wrong data entered")
79 sys.exit()
80 # step 5
81 year = int(dob[0:4])
82 month = int(dob[4:6])
83 day = int(dob[6:])
84 # step 6
85 result = range_check(year,(1900,9999))
86 if result == False:
87 print("Error 10: year out of range, must be 1900 or later")
88 sys.exit()
89 result = range_check(month,(1,12))
90 if result == False:
91 print("Error 02: Wrong month entered")
92 sys.exit()
93 result = leap_year(year)
94 if result == True:
95 days_in_month[2] = 29
96 result = range_check(day, (1, days_in_month[month]))
97 if result == False:
98 print("Error 03: wrong day entered")
99 sys.exit()
100 # step 7
101 new_dob = str(month_name[month - 1])+' '+ str(day)+', '+str(year)
102 # step 8
103 print("Your date of birth is:", new_dob)
(Pdb)set the break point with 'b' or 'break'
Next, let set a break points at line 66 and 72:
(Pdb) b 66
Breakpoint 1 at /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py:66
(Pdb) b 72
Breakpoint 2 at /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py:72At anytime, you can display all the break points and their status with just the 'b' or 'break' command:
(Pdb) b
Num Type Disp Enb Where
1 breakpoint keep yes at /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py:66
2 breakpoint keep yes at /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py:72Use the 'n' command to execute the next Python statement
Here are the step-by-step execution of your Python script:
> /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py(2)<module>()
-> ''' template for ops435 assignment 1 script
(Pdb) n
> /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py(18)<module>()
-> import os
(Pdb) n
> /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py(19)<module>()
-> import sys
(Pdb) n
> /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py(21)<module>()
-> def leap_year(obj):
(Pdb) n
> /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py(29)<module>()
-> def sanitize(obj1,obj2):
(Pdb) n
> /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py(37)<module>()
-> def size_check(obj, intobj):
(Pdb) n
> /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py(45)<module>()
-> def range_check(obj1, obj2):
(Pdb) n
> /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py(53)<module>()
-> def usage():
(Pdb) n
> /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py(60)<module>()
-> if __name__ == "__main__":
(Pdb) n
> /home/rchan/Desktop/ops435/2020-03/a1/ops435-a1/a1_template.py(62)<module>()
-> if len(sys.argv) != 2:
(Pdb)Please try it your self to have some fun!
