python 第8章 异常处理

Python 用异常对象来表示异常，遇到错误会引发异常程序回溯。python已经建立了许多的异常类方法，用户自己也建立自己异常类型

8.2.1 raise语句

如果不是继承的Exception的类或方法，想处理异常就需要借助ｒａｉｓｅ语句

>>> raise "The information of error"

Traceback (most recent call last):
File "<pyshell#17>", line 1, in <module>
raise "The information of error"
TypeError: exceptions must be old-style classes or derived from BaseException, not str
>>>

>>> import exceptions
>>> dir(exceptions)
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BufferError', 'BytesWarning', 'DeprecationWarning', 'EOFError', 'EnvironmentError', 'Exception', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'NameError', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'ReferenceError', 'RuntimeError', 'RuntimeWarning', 'StandardError', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'WindowsError', 'ZeroDivisionError', '__doc__', '__name__', '__package__']

8.3 捕捉异常

>>> x = input()
10
>>> y = input()
0
>>> try:
z=x/y
print z
except ZeroDivisionError:
print "The num is zero!!!"

The num is zero!!!

屏蔽异常

class MuffledCalculator:
muffled = False
def calc(self,expr):
try:
return eval(expr)
except ZeroDivisionError:
if self.muffled:
print 'illegal divided by zero'
else:
raise

z = MuffledCalculator()
z.muffled = True
print z.calc("6/0")
z.muffled = False
print z.calc("6/0")

>>>

illegal divided by zero

None

Traceback (most recent call last):

File "G:/New Knowledge/practice/python/test.py", line 16, in <module>

print z.calc("6/0")

File "G:/New Knowledge/practice/python/test.py", line 5, in calc

return eval(expr)

File "<string>", line 1, in <module>

ZeroDivisionError: integer division or modulo by zero

>>>

class MuffledCalculator:
muffled = False
def calc(self,expr):
try:
return eval(expr)
except ZeroDivisionError:
if self.muffled:
print 'illegal divided by zero'
else:
raise
except (TypeError,NameError),e:
print e

z = MuffledCalculator()
z.muffled = True
print z.calc("6/0")
z.muffled = False
print z.calc("7/3")
print z.calc("count")

>>>

illegal divided by zero

None

2

name 'count' is not defined

None

>>>

def cal(x,y):
try:
print x/y
except NameError:
print "unknown name"
except ZeroDivisionError:
print 'zero divided'
else:
print "go on well"
finally:
print "cleaning up"

>>> cal(4,3)

1

go on well

cleaning up

>>> cal(4,0)

zero divided

cleaning up

>>> cal('3','sd')

cleaning up

Traceback (most recent call last):

File "<pyshell#47>", line 1, in <module>

cal('3','sd')

File "<pyshell#43>", line 3, in cal

print x/y

TypeError: unsupported operand type(s) for /: 'str' and 'str'

>>>

异常传递：

def faulty():
raise Exception('Someting is wrong!!!')
def ignore_exception():
faulty()
def handle_exception():
try:
faulty()
except:
print 'error in handle'

handle_exception()
ignore_exception()

error in handle

Traceback (most recent call last):

File "G:/New Knowledge/practice/python/test.py", line 12, in <module>

ignore_exception()

File "G:/New Knowledge/practice/python/test.py", line 4, in ignore_exception

faulty()

File "G:/New Knowledge/practice/python/test.py", line 2, in faulty

raise Exception('Someting is wrong!!!')

Exception: Someting is wrong!!!

>>>

8.11 运用异常：

def describePerson1(person):
print "Description of ",person['name']
print 'age:%(age)s'%person
if 'Occupation' in person:
print 'Occupation:%(Occupation)s'%person

def describePerson2(person):
print "Description of ",person['name']
print 'age:%(age)s'%person
try:
print 'Occupation:%(Occupation)s'%person
except:pass

d = {'name':'John','age':15,'Occupation':'student'}
t = {'name':'John','age':15}
describePerson1(d)
describePerson1(t)
describePerson2(d)
describePerson2(t)

使用异常，效率更高

>>>

Description of John

age:15

Occupation:student

Description of John

age:15

Description of John

age:15

Occupation:student

Description of John

age:15

>>>