# err.py
def foo(s):
  n = int(s)
  print '>>> n = %d' % n
  return 10 / n

def main():
  foo('0')

main()

$ python err.py
>>> n = 0
Traceback (most recent call last):
 ...
ZeroDivisionError: integer division or modulo by zero

# err.py
def foo(s):
  n = int(s)
  assert n != 0, 'n is zero!'
  return 10 / n

def main():
  foo('0')

$ python err.py
Traceback (most recent call last):
 ...
AssertionError: n is zero!

$ python -O err.py
Traceback (most recent call last):
 ...
ZeroDivisionError: integer division or modulo by zero

# err.py
import logging

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

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

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

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

$ python -m pdb err.py
> /Users/michael/Github/sicp/err.py(2)<module>()
-> s = '0'

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

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

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

(Pdb) n
ZeroDivisionError: 'integer division or modulo by zero'
> /Users/michael/Github/sicp/err.py(4)<module>()
-> print 10 / n
(Pdb) q

# err.py
import pdb

s = '0'
n = int(s)
pdb.set_trace() # 运行到这里会自动暂停
print 10 / n

$ python err.py 
> /Users/michael/Github/sicp/err.py(7)<module>()
-> print 10 / n
(Pdb) p n
0
(Pdb) c
Traceback (most recent call last):
 File "err.py", line 7, in <module>
  print 10 / n
ZeroDivisionError: integer division or modulo by zero