何でもかんでも捕まえる

>>> import sys
>>> import traceback
>>> try:
...   a = 1 / 0
... except:
...   print "exc_info: %s" % str(sys.exc_info())
...   print "[0]: %s" % sys.exc_info()[0]
...   print "[1]: %s" % sys.exc_info()[1]
...   traceback.print_tb(sys.exc_info()[2])
... 
exc_info: (<class exceptions.ZeroDivisionError at 0x83267f4>, <exceptions.ZeroDivisionError instance at 0x8345104>, ^<traceback object at 0x834674c>)
[0]: exceptions.ZeroDivisionError
[1]: integer division or modulo by zero
  File "<stdin>", line 2, in ?
>>>

特定のものを捕まえる

>>> try:
...   a = 1 / 0
... except ValueError, NameError:
...   print "exception occurred."
... except ZeroDivisionError:
...   print "Illegal division by zero."
... 
Illegal division by zero.
>>> 

トレースバックの取得

>>> try:
...   a = 1 / 0
... except ZeroDivisionError:
...   traceback.print_exc(file=sys.stdout)
...   print "----------"
...   raise
... 
Traceback (most recent call last):
  File "<stdin>", line 2, in ?
ZeroDivisionError: integer division or modulo by zero
----------
Traceback (most recent call last):
  File "<stdin>", line 2, in ?
ZeroDivisionError: integer division or modulo by zero
>>> 

else

例外にならないときだけ処理することを書く。
トラップしたい例外が起こるところだけをtryブロックに書く。

>>> 
>>> try:
...   print "no exception"
... except:
...   traceback.print_exc(file=sys.stdout)
... else:
...   print "exception not occurred."
... 
no exception
exception not occurred.
>>>

finally

例外になろうがなるまいが処理することを書く。

>>> 
>>> try:
...   print 1 / 0
... finally:
...   print "a"
... 
a
Traceback (most recent call last):
  File "<stdin>", line 2, in ?
ZeroDivisionError: integer division or modulo by zero
>>> 

ユーザー定義の例外

例外オブジェクト(?)の中身(?)

>>> try:
...   hash = {}
...   print hash['ABCDE']
... except:
...   print "0: %s" % sys.exc_info()[0]
...   print "1: %s" % sys.exc_info()[1]
...   traceback.print_tb(sys.exc_info()[2])
... 
0: exceptions.KeyError
1: ABCDE
  File "<stdin>", line 3, in ?
>>> 

名前だけ指定して発生させた場合

>>> try:
...   raise "1234567"
... except:
...   
...   print "0: %s" % sys.exc_info()[0]
...   print "1: %s" % sys.exc_info()[1]
...   traceback.print_tb(sys.exc_info()[2])
... 
0: 1234567
1: None
  File "<stdin>", line 2, in ?
>>> 

2番目の項目にも何かセットしたい場合は以下。二つ指定する。引数は3つ必要らしい。

>>> try:
...   raise "1234567", 'acbde'
... except:
...   print "0: %s" % sys.exc_info()[0]
...   print "1: %s" % sys.exc_info()[1]
...   traceback.print_tb(sys.exc_info()[2])
... 
0: 1234567
1: acbde
  File "<stdin>", line 1, in ?
>>>