Introduction to Debugging in Python

• Author: Craig Maloney
• Email: craig@decafbad.net
• Website: http://decafbad.net
• Presented: 2017-04-29

Programming is hard

Programming leads to bugs

Not all bugs are as obvious

Debugging is not just about fixing bugs...

Debugging is about matching our expectations of what the code should be doing with the reality of what the computer is executing.

What does this code do?

# Example 1
def main():

    # Obviously bad code follows
    for i in range(1, 20):
        i /= 4

    if i == 20:
        print("Completed")

if __name__ == "__main__":
    main()

Let's execute it and see what this does

craig@lister:~/projects/intro_debugging_python$ env/bin/python3 example1.py
craig@lister:~/projects/intro_debugging_python$

So, what happened?

# Example 1
def main():

    # Obviously bad code follows
    for i in range(1, 20):
        i /= 4

    if i == 20:
        print("Completed")

if __name__ == "__main__":
    main()

When we run this nothing is displayed.

The lowly print() statement

# Example 2
def main():

    # Obviously bad code follows
    for i in range(1, 20):
        i /= 4
        print(i)

    if i == 20:
        print("Completed")

if __name__ == "__main__":
    main()

craig@lister:~/projects/intro_debugging_python$ python3 example2.py
0.25
0.5
0.75
1.0
1.25
1.5
1.75
2.0
2.25
2.5
2.75
3.0
3.25
3.5
3.75
4.0
4.25
4.5
4.75

Now we can see what's happening with the i variable.

What we learned...

• print(i) shows us the value inside of i
• i is reset each iteration by the range(1, 20) generator.
• i will never be equal to 20 in this program, so we have dead code.

Switching over to logging...

import logging

# Example 3
def main():

    logging.basicConfig(filename='example.log', level=logging.DEBUG)

    # Obviously bad code follows
    logging.debug("Beginning Loop")
    for i in range(1, 20):
        i /= 4
        logging.debug(i)
    logging.debug("End Loop")

    if i == 20:
        print("Completed")
        logging.debug("Completed")

    logging.debug("End program")

if __name__ == "__main__":
    main()

We're back to

"silent running"...

But now we have a log file of the results...

example.log:

DEBUG:root:Beginning Loop
DEBUG:root:0.25
DEBUG:root:0.5
DEBUG:root:0.75
DEBUG:root:1.0
DEBUG:root:1.25
DEBUG:root:1.5
DEBUG:root:1.75
DEBUG:root:2.0
DEBUG:root:2.25
DEBUG:root:2.5
DEBUG:root:2.75
DEBUG:root:3.0
DEBUG:root:3.25
DEBUG:root:3.5
DEBUG:root:3.75
DEBUG:root:4.0
DEBUG:root:4.25
DEBUG:root:4.5
DEBUG:root:4.75
DEBUG:root:End Loop
DEBUG:root:End program

So, what does this get us?

Using logging gives us the ability to:

• Turn debugging messages off and on again
• Not have to modify all of our code to turn debug messages on or off
• Filter which messages are logged and which are silently ignored

import logging


# Example 4
def main():

    logging.basicConfig(level=logging.INFO)

    logging.info("Beginning program")

    # Obviously bad code follows
    logging.debug("Beginning Loop")
    for i in range(1, 20):
        i /= 4
        logging.debug(i)
    logging.debug("End Loop")

    if i == 20:
        print("Completed")
        logging.debug("Completed")

    logging.info("End program")

if __name__ == "__main__":
    main()

craig@lister:~/projects/intro_debugging_python$ python example4.py
INFO:root:Beginning program
INFO:root:End program

craig@lister:~/projects/intro_debugging_python$ git diff example4.py
diff --git a/example4.py b/example4.py
index 8b75c70..08824ee 100644
--- a/example4.py
+++ b/example4.py
@@ -4,7 +4,7 @@ import logging
# Example 4
def main():

-    logging.basicConfig(level=logging.INFO)
+    logging.basicConfig(level=logging.DEBUG)

    logging.info("Beginning program")

craig@lister:~/projects/intro_debugging_python$ python3 example4.py
INFO:root:Beginning program
DEBUG:root:Beginning Loop
DEBUG:root:0.25
DEBUG:root:0.5
DEBUG:root:0.75
DEBUG:root:1.0
DEBUG:root:1.25
DEBUG:root:1.5
DEBUG:root:1.75
DEBUG:root:2.0
DEBUG:root:2.25
DEBUG:root:2.5
DEBUG:root:2.75
DEBUG:root:3.0
DEBUG:root:3.25
DEBUG:root:3.5
DEBUG:root:3.75
DEBUG:root:4.0
DEBUG:root:4.25
DEBUG:root:4.5
DEBUG:root:4.75
DEBUG:root:End Loop
INFO:root:End program

So our debugging messages can be turned on and off at will

Let's try another example...

# sum_of_numbers.py
def main():
    list_of_numbers = []
    with open("list_of_numbers", 'rt') as f:
        for number in f:
            list_of_numbers.append(number)

    print("The sum is {total}".format(total=sum(list_of_numbers)))

if __name__ == "__main__":
    main()

Running the code...

craig@lister:~/projects/intro_debugging_python$ env/bin/python3 sum_of_numbers.py
Traceback (most recent call last):
File "sum_of_numbers.py", line 11, in <module>
    main()
File "sum_of_numbers.py", line 8, in main
    print("The sum is {total}".format(total=sum(list_of_numbers)))
TypeError: unsupported operand type(s) for +: 'int' and 'str'

So, what happened?

Sure we could log or print the data, but...

craig@lister:~/projects/intro_debugging_python$ wc -l list_of_numbers
2000001 list_of_numbers

That's two million and one records.

That's a LOT of data to wade through...

One approach...

# sum_of_numbers.py
def main():
    list_of_numbers = []
    with open("list_of_numbers", 'rt') as f:
        for number in f:
            list_of_numbers.append(number)

    # Print out the first element for debugging
    print(list_of_numbers[0])

    print("The sum is {total}".format(total=sum(list_of_numbers)))

if __name__ == "__main__":
    main()

craig@lister:~/projects/intro_debugging_python$ env/bin/python3 sum_of_numbers.py
24601

Traceback (most recent call last):
File "sum_of_numbers.py", line 13, in <module>
    main()
File "sum_of_numbers.py", line 10, in main
    print("The sum is {total}".format(total=sum(list_of_numbers)))
TypeError: unsupported operand type(s) for +: 'int' and 'str'

So, that sort of worked?

# sum_of_numbers.py
def main():
    list_of_numbers = []
    with open("list_of_numbers", 'rt') as f:
        for number in f:
            list_of_numbers.append(number)

    # Print out debugging information for first element
    print(list_of_numbers[0])
    print(type(list_of_numbers[0]))

    print("The sum is {total}".format(total=sum(list_of_numbers)))

if __name__ == "__main__":
    main()

craig@lister:~/projects/intro_debugging_python$ env/bin/python3 sum_of_numbers.py
24601

<class 'str'>
Traceback (most recent call last):
File "sum_of_numbers.py", line 14, in <module>
    main()
File "sum_of_numbers.py", line 11, in main
    print("The sum is {total}".format(total=sum(list_of_numbers)))
TypeError: unsupported operand type(s) for +: 'int' and 'str'

print() is a blunt instrument

Even logging isn't of much help:

# sum_of_numbers.py
import logging


def main():
    logging.basicConfig(level=logging.DEBUG)

    list_of_numbers = []
    with open("list_of_numbers", 'rt') as f:
        for number in f:
            list_of_numbers.append(number)

    # Print out debugging information for first element
    logging.debug(list_of_numbers[0])
    logging.debug(type(list_of_numbers[0]))

    print("The sum is {total}".format(total=sum(list_of_numbers)))

if __name__ == "__main__":
    main()

craig@lister:~/projects/intro_debugging_python$ env/bin/python3 sum_of_numbers.py
DEBUG:root:24601

DEBUG:root:<class 'str'>
Traceback (most recent call last):
File "sum_of_numbers.py", line 19, in <module>
    main()
File "sum_of_numbers.py", line 16, in main
    print("The sum is {total}".format(total=sum(list_of_numbers)))
TypeError: unsupported operand type(s) for +: 'int' and 'str'
craig@lister:~/projects/intro_debugging_python$

Enter the debugger

craig@lister:~/projects/intro_debugging_python$ env/bin/python -m pdb sum_of_numbers.py
> /home/craig/projects/intro_debugging_python/sum_of_numbers.py(4)<module>()
-> def main():
(Pdb) b 11
Breakpoint 1 at /home/craig/projects/intro_debugging_python/sum_of_numbers.py:11
(Pdb) l
1   # sum_of_numbers.py
2
3
4  ->       def main():
5
6       list_of_numbers = []
7       with open("list_of_numbers", 'rt') as f:
8           for number in f:
9               list_of_numbers.append(number)
10
11 B            print("The sum is {total}".format(total=sum(list_of_numbers)))
(Pdb) c
> /home/craig/projects/intro_debugging_python/sum_of_numbers.py(11)main()
-> print("The sum is {total}".format(total=sum(list_of_numbers)))
(Pdb)

craig@lister:~/projects/intro_debugging_python$ env/bin/python -m pdb sum_of_numbers.py
> /home/craig/projects/intro_debugging_python/sum_of_numbers.py(4)<module>()
-> def main():
(Pdb) b 11
Breakpoint 1 at /home/craig/projects/intro_debugging_python/sum_of_numbers.py:11
(Pdb) l
1   # sum_of_numbers.py
2
3
4  ->       def main():
5
6       list_of_numbers = []
7       with open("list_of_numbers", 'rt') as f:
8           for number in f:
9               list_of_numbers.append(number)
10
11 B            print("The sum is {total}".format(total=sum(list_of_numbers)))
(Pdb) c
> /home/craig/projects/intro_debugging_python/sum_of_numbers.py(11)main()
-> print("The sum is {total}".format(total=sum(list_of_numbers)))
(Pdb) p list_of_numbers[0]
'24601\n'
(Pdb)

Cheatsheet

https://github.com/nblock/pdb-cheatsheet

Invoking the Debugger

• python -m pdb filename.py
• In the sourcecode itself:
  • import pdb;pdb.set_trace()

# sum_of_numbers.py


def main():

    list_of_numbers = []
    with open("list_of_numbers", 'rt') as f:
        for number in f:
            list_of_numbers.append(number)

    # Start the debugger here
    import pdb
    pdb.set_trace()

    print("The sum is {total}".format(total=sum(list_of_numbers)))

if __name__ == "__main__":
    main()

craig@lister:~/projects/intro_debugging_python$ env/bin/python3 sum_of_numbers.py
> /home/craig/projects/intro_debugging_python/sum_of_numbers.py(14)main()
-> print("The sum is {total}".format(total=sum(list_of_numbers)))
(Pdb)

OK, back to debugging the code...

# sum_of_numbers.py


def main():

    import pdb
    pdb.set_trace()

    list_of_numbers = []
    with open("list_of_numbers", 'rt') as f:
        for number in f:
            # Convert input to an integer
            list_of_numbers.append(int(number))

    print("The sum is {total}".format(total=sum(list_of_numbers)))

if __name__ == "__main__":
    main()

We convert number to an integer...

craig@lister:~/projects/intro_debugging_python$ env/bin/python3 integer_sum_of_numbers.py
> /home/craig/projects/intro_debugging_python/integer_sum_of_numbers.py(9)main()
-> list_of_numbers = []
(Pdb) c
Traceback (most recent call last):
File "integer_sum_of_numbers.py", line 18, in <module>
    main()
File "integer_sum_of_numbers.py", line 9, in main
    list_of_numbers = []
ValueError: invalid literal for int() with base 10: 'Bob\n'

What the @#$%?!

Conditional Breakpoint

(Pdb) b 13, number == 'Bob\n'
Breakpoint 1 at /home/craig/projects/intro_debugging_python/integer_sum_of_numbers.py:13
(Pdb) c
> /home/craig/projects/intro_debugging_python/integer_sum_of_numbers.py(13)main()
-> list_of_numbers.append(int(number))
(Pdb) p number
'Bob\n'
(Pdb) l
8
9       list_of_numbers = []
10              with open("list_of_numbers", 'rt') as f:
11                  for number in f:
12                      # Convert input to an integer
13 B->                  list_of_numbers.append(int(number))
14
15              print("The sum is {total}".format(total=sum(list_of_numbers)))
16
17          if __name__ == "__main__":
18              main()
(Pdb)

Someone left a stray "Bob" in the data

(Dammit Bob, get out of the data)

So, how do we work around this?

One approach...

# sum_of_numbers.py


def main():

    import pdb
    pdb.set_trace()

    list_of_numbers = []
    with open("list_of_numbers", 'rt') as f:
        for number in f:
            try:
                # Convert input to an integer
                list_of_numbers.append(int(number))
            except ValueError:
                pass

    print("The sum is {total}".format(total=sum(list_of_numbers)))

if __name__ == "__main__":
    main()

craig@lister:~/projects/intro_debugging_python$ env/bin/python3 integer_sum_of_numbers.py
> /home/craig/projects/intro_debugging_python/integer_sum_of_numbers.py(9)main()
-> list_of_numbers = []
(Pdb) c
The sum is 30009298902

Let's do one better...

# sum_of_numbers.py

import logging


def main():

    logging.basicConfig(level=logging.INFO)
    list_of_numbers = []
    with open("list_of_numbers", 'rt') as f:
        for number in f:
            try:
                # Convert input to an integer
                list_of_numbers.append(int(number))
            except ValueError:
                logging.warning("Received non-integer input")
                logging.warning(number)

    print("The sum is {total}".format(total=sum(list_of_numbers)))

if __name__ == "__main__":
    main()

craig@lister:~/projects/intro_debugging_python$ env/bin/python3 integer_sum_of_numbers.py
WARNING:root:Received non-integer input
WARNING:root:Bob

The sum is 30009298902

Now we're logging a warning whenever we get non-integer data

(Thanks a lot, Bob)

So, what have we learned?

What we've learned:

• We can invoke the Python Debugger on our code
  • python3 -m pdb filename.py
  • import pdb;pdb.set_trace()
• We can set breakpoints in our code
• We can use conditionals for breakpoints

Let's look more at debugging real computer code...

def fib(n):
    if n == 1:
        return 1
    elif n == 0:
        return 0
    else:
        return fib(n-1) + fib(n-2)


def main():
    print(fib(10))


if __name__ == '__main__':
    main()

Let's see what this code does...

craig@bluemidget:~/projects/intro_debugging_python$ python3 -m pdb fib.py
> /home/craig/projects/intro_debugging_python/fib.py(1)<module>()
-> def fib(n):
(Pdb) b 7
Breakpoint 1 at /home/craig/projects/intro_debugging_python/fib.py:7
(Pdb) ll
1  -> def fib(n):
2         if n == 1:
3             return 1
4         elif n == 0:
5             return 0
6         else:
7 B           return fib(n-1) + fib(n-2)
8
9
10     def main():
11         print(fib(10))
12
13
14     if __name__ == '__main__':
15         main()

Repetitious commands around breakpoints...

Wouldn't it be nice to see the call stack and the current arguments of the current method call?

(Pdb) commands 1
(com) bt
(com) args
(com) end
(Pdb)

(Pdb) b 5
Breakpoint 2 at /home/craig/projects/intro_debugging_python/fib.py:5
(Pdb) commands 2
(com) bt
(com) end
(Pdb) b 3
Breakpoint 3 at /home/craig/projects/intro_debugging_python/fib.py:3
(Pdb) commands 3
(com) bt
(com) end

(Pdb) ll
1  ->       def fib(n):
2       if n == 1:
3 B         return 1
4       elif n == 0:
5 B         return 0
6       else:
7 B         return fib(n-1) + fib(n-2)
8
9
10          def main():
11              print(fib(10))
12
13
14          if __name__ == '__main__':
15              main()

(Pdb) b
Num Type         Disp Enb   Where
1   breakpoint   keep yes   at /home/craig/projects/intro_debugging_python/fib.py:7
2   breakpoint   keep yes   at /home/craig/projects/intro_debugging_python/fib.py:3
3   breakpoint   keep yes   at /home/craig/projects/intro_debugging_python/fib.py:5

(Pdb) c
/usr/lib/python3.4/bdb.py(431)run()
-> exec(cmd, globals, locals)
<string>(1)<module>()
/home/craig/projects/intro_debugging_python/fib.py(15)<module>()
-> main()
/home/craig/projects/intro_debugging_python/fib.py(11)main()
-> print(fib(10))
> /home/craig/projects/intro_debugging_python/fib.py(7)fib()
-> return fib(n-1) + fib(n-2)
n = 10
> /home/craig/projects/intro_debugging_python/fib.py(7)fib()
-> return fib(n-1) + fib(n-2)
(Pdb) l
2       if n == 1:
3           return 1
4       elif n == 0:
5           return 0
6       else:
7 B->               return fib(n-1) + fib(n-2)
8
9
10          def main():
11              print(fib(10))
12

Time passes...

(Pdb) c
/usr/lib/python3.4/bdb.py(431)run()
-> exec(cmd, globals, locals)
<string>(1)<module>()
/home/craig/projects/intro_debugging_python/fib.py(15)<module>()
-> main()
/home/craig/projects/intro_debugging_python/fib.py(11)main()
-> print(fib(10))
/home/craig/projects/intro_debugging_python/fib.py(7)fib()
-> return fib(n-1) + fib(n-2)
...
-> return fib(n-1) + fib(n-2)
> /home/craig/projects/intro_debugging_python/fib.py(7)fib()
-> return fib(n-1) + fib(n-2)
n = 2
> /home/craig/projects/intro_debugging_python/fib.py(7)fib()
-> return fib(n-1) + fib(n-2)
(Pdb) c

(Pdb) c
/usr/lib/python3.4/bdb.py(431)run()
-> exec(cmd, globals, locals)
<string>(1)<module>()
/home/craig/projects/intro_debugging_python/fib.py(15)<module>()
-> main()
/home/craig/projects/intro_debugging_python/fib.py(11)main()
-> print(fib(10))
/home/craig/projects/intro_debugging_python/fib.py(7)fib()
-> return fib(n-1) + fib(n-2)
...
 /home/craig/projects/intro_debugging_python/fib.py(7)fib()
-> return fib(n-1) + fib(n-2)
> /home/craig/projects/intro_debugging_python/fib.py(3)fib()
-> return 1
> /home/craig/projects/intro_debugging_python/fib.py(3)fib()
-> return 1

(Pdb) c
/usr/lib/python3.4/bdb.py(431)run()
-> exec(cmd, globals, locals)
<string>(1)<module>()
/home/craig/projects/intro_debugging_python/fib.py(15)<module>()
-> main()
/home/craig/projects/intro_debugging_python/fib.py(11)main()
-> print(fib(10))
/home/craig/projects/intro_debugging_python/fib.py(7)fib()
-> return fib(n-1) + fib(n-2)
...
/home/craig/projects/intro_debugging_python/fib.py(7)fib()
-> return fib(n-1) + fib(n-2)
> /home/craig/projects/intro_debugging_python/fib.py(5)fib()
-> return 0
> /home/craig/projects/intro_debugging_python/fib.py(5)fib()
-> return 0

Demo...

What we learned...

What we learned...

• Breakpoints can have commands associated with them using commands <breakpoint number>
• args displays the arguments passed to the method
• bt and where show the stack trace
• c continues after reaching a break point
• u and d move up and down the stack (demo)

A few more commands...

def pointless_loop(n):

    number_sum = 0
    # This is a pointless loop
    for i in range(1, n+1):
        number_sum += i


def main():
    pointless_loop(30)

if __name__ == '__main__':
    main()

Next and Step

n: runs the next line of the code s: steps into a function

Demo

Conditional breakpoint...

b <linenum> , <condition>

b 6, number_sum > 100

craig@bluemidget:~/projects/intro_debugging_python$ python3 -m pdb pointless_loop.py
> /home/craig/projects/intro_debugging_python/pointless_loop.py(1)<module>()
-> def pointless_loop(n):
(Pdb) ll
1  ->       def pointless_loop(n):
2
3       number_sum = 0
4       # This is a pointless loop
5       for i in range(1, n+1):
6           number_sum += i
...
(Pdb) b 6, number_sum > 100
Breakpoint 1 at /home/craig/projects/intro_debugging_python/pointless_loop.py:6
(Pdb) commands 1
(com) pp i
(com) pp number_sum
(com) end
(Pdb) c
15
105
> /home/craig/projects/intro_debugging_python/pointless_loop.py(6)pointless_loop()
-> number_sum += i

> /home/craig/projects/intro_debugging_python/pointless_loop.py(6)pointless_loop()
-> number_sum += i
(Pdb) c
16
120
> /home/craig/projects/intro_debugging_python/pointless_loop.py(6)pointless_loop()
-> number_sum += i
(Pdb) c
17
136
> /home/craig/projects/intro_debugging_python/pointless_loop.py(6)pointless_loop()
-> number_sum += i
(Pdb) b
Num Type         Disp Enb   Where
1   breakpoint   keep yes   at /home/craig/projects/intro_debugging_python/pointless_loop.py:6
    stop only if number_sum > 100
    breakpoint already hit 17 times

Disabling Breakpoints...

disable <breakpoint number>

disable 1

> /home/craig/projects/intro_debugging_python/pointless_loop.py(6)pointless_loop()
-> number_sum += i
(Pdb) c
22
231
> /home/craig/projects/intro_debugging_python/pointless_loop.py(6)pointless_loop()
-> number_sum += i
(Pdb) c
23
253
> /home/craig/projects/intro_debugging_python/pointless_loop.py(6)pointless_loop()
-> number_sum += i
(Pdb) disable 1
Disabled breakpoint 1 at /home/craig/projects/intro_debugging_python/pointless_loop.py:6
(Pdb) b
Num Type         Disp Enb   Where
1   breakpoint   keep no    at /home/craig/projects/intro_debugging_python/pointless_loop.py:6
    stop only if number_sum > 100
    breakpoint already hit 23 times

Temporary Breakpoints...

(Pdb) tbreak 6, number_sum > 100
Breakpoint 1 at /home/craig/projects/intro_debugging_python/pointless_loop.py:6
(Pdb) l
1  ->       def pointless_loop(n):
2
3       number_sum = 0
4       # This is a pointless loop
5       for i in range(1, n+1):
6 B         number_sum += i
...
(Pdb) b
Num Type         Disp Enb   Where
1   breakpoint   del  yes   at /home/craig/projects/intro_debugging_python/pointless_loop.py:6
    stop only if number_sum > 100
(Pdb) c
Deleted breakpoint 1 at /home/craig/projects/intro_debugging_python/pointless_loop.py:6
> /home/craig/projects/intro_debugging_python/pointless_loop.py(6)pointless_loop()
-> number_sum += i
(Pdb) pp number_sum
105
(Pdb) b
(Pdb)

What we learned

What we learned...

• next and step can navigate through the code
• Breakpoints can be conditionally triggered
• c can also continue from where we left off in the code
• Breakpoints may be disabled so they no longer fire
• Temporary Breakpoints may be set so they are deleted once they are hit

Python3 Debugging Goodies...

Display

> /home/craig/projects/intro_debugging_python/pointless_loop.py(1)<module>()
-> def pointless_loop(n):
(Pdb) n
> /home/craig/projects/intro_debugging_python/pointless_loop.py(9)<module>()
-> def main():
(Pdb) n
> /home/craig/projects/intro_debugging_python/pointless_loop.py(12)<module>()
-> if __name__ == '__main__':
(Pdb) n
> /home/craig/projects/intro_debugging_python/pointless_loop.py(13)<module>()
-> main()
(Pdb) s
--Call--
> /home/craig/projects/intro_debugging_python/pointless_loop.py(9)main()
-> def main():
(Pdb) n

> /home/craig/projects/intro_debugging_python/pointless_loop.py(10)main()
-> pointless_loop(30)
(Pdb) s
--Call--
> /home/craig/projects/intro_debugging_python/pointless_loop.py(1)pointless_loop()
-> def pointless_loop(n):
(Pdb) display number_sum
display number_sum: ** raised NameError: name 'number_sum' is not defined **
(Pdb) n
> /home/craig/projects/intro_debugging_python/pointless_loop.py(3)pointless_loop()
-> number_sum = 0
(Pdb) n
> /home/craig/projects/intro_debugging_python/pointless_loop.py(5)pointless_loop()
-> for i in range(1, n+1):
display number_sum: 0  [old: ** raised NameError: name 'number_sum' is not defined **]
(Pdb)

(Pdb) n
> /home/craig/projects/intro_debugging_python/pointless_loop.py(6)pointless_loop()
-> number_sum += i
(Pdb) n
> /home/craig/projects/intro_debugging_python/pointless_loop.py(5)pointless_loop()
-> for i in range(1, n+1):
display number_sum: 1  [old: 0]
(Pdb) n
> /home/craig/projects/intro_debugging_python/pointless_loop.py(6)pointless_loop()
-> number_sum += i
(Pdb) n
> /home/craig/projects/intro_debugging_python/pointless_loop.py(5)pointless_loop()
-> for i in range(1, n+1):
display number_sum: 3  [old: 1]
(Pdb) n
> /home/craig/projects/intro_debugging_python/pointless_loop.py(6)pointless_loop()
-> number_sum += i
(Pdb) n
> /home/craig/projects/intro_debugging_python/pointless_loop.py(5)pointless_loop()
-> for i in range(1, n+1):
display number_sum: 6  [old: 3]
(Pdb) n

Pdb++

https://pypi.python.org/pypi/pdbpp/

Demo...

Helpful links...

Pdb Debugger:

• https://pymotw.com/3/pdb/
• https://github.com/nblock/pdb-cheatsheet
• https://docs.python.org/3/library/pdb.html

Logging:

• https://pymotw.com/3/logging/
• https://docs.python.org/3/library/logging.html

Pdb++:

• https://pypi.python.org/pypi/pdbpp/

Questions?

Thank you!

Introduction to Debugging in Python

• Author: Craig Maloney
• Email: craig@decafbad.net
• Website: http://decafbad.net
• Presented: 2017-04-29