python中的异常处理
什么是异常?
在程序运行过程中影响程序正常运行的内容，
为什么需要异常处理?
可以让你的程序更加健壮， 可以清晰的快速修复异常。
1). print(s)
NameError: name 's' is not defined
2). li = [1,2,3]
li[10]
IndexError: list index out of range
3). 10/0
ZeroDivisionError: division by zero
>>> d = dict(a=1, b=2)
>>> d
{'a': 1, 'b': 2}
>>> d['c']
Traceback (most recent call last):
File "", line 1, in
KeyError: 'c'
4).d = dict(a=1, b=2)
d
{'a': 1, 'b': 2}
d['c']
KeyError: 'c'
5).
AttributeError: 'Student' object has no attribute 'scores'
# print(s)
class Student(object):
def __init__(self, name, age):
self.name = name
self.age = age
def echo(self):
return self.name
def __str__(self):
return "Student(%s)" %(self.name)
s = Student('黎明', 30)
# print(s.scores)
# s.echo1()
# FileNotFoundError: [Errno 2] No such file or directory: '/tmp/aa'
with open('/tmp/aa') as f:
print(f.read()[:10])
try…except… else…finally…
普通的异常处理：
import time
try:
# 如果你觉得代码可能出现问题，那么放在try语句中，只执行一次；
print(s)
# print("hello")
except NameError as e: # 对于异常进行一个重命名；记录了异常的详细信息；
# 可能执行一次， 也可能不执行；
print("名称错误")
with open("except.log", 'w') as f:
f.write(time.ctime() + ' ')
f.write(str(e))
finally:
# 无论是否出现异常， 肯定会执行一次，
print("处理结束")
import time
try:
# 如果你觉得代码可能出现问题， 那么放在try语句中， 只执行一次；
print('hello')
with open('/etc/aa') as f:
print(f.read()[:5])
print("文件读取结束")
li = [1, 2, 3, 4] # try语句中一旦出现问题， 后面的语句(try里面的)不执行
print(li[5])
print(s)
print("hello")
except (NameError, IndexError) as e: # 对于异常进行一个重命名；记录了异常的详细信息；
# 可能执行一次， 也可能不执行；
# print("名称错误")
with open("except.log", 'a+') as f:
f.write(time.ctime() + ' ' + str(e) + '\n')
finally:
# 无论是否出现异常， 肯定会执行一次，
print("处理结束")
官方实例
# 1).
class B(Exception):
pass
class C(B):
pass
class D(C):
pass
for cls in [B, C, D]:
try:
raise cls()
except D:
print("D")
except C:
print("C")
except B:
print("B")
# 2).
import sys
# /etc/passwd /etc/group
for arg in sys.argv[1:]:
try:
f = open(arg, 'r')
except OSError:
print('cannot open', arg)
else:
# 如果try语句中没有产生任何异常和错误， 才执行的语句；
print(arg, 'has', len(f.readlines()), 'lines')
f.close()
抛出异常
age = int(input("Age:"))
# try....except...finally ===== 捕获异常
# raise ====== 抛出异常
class AgeError(Exception):
pass
if age < 0 or age > 120:
raise AgeError
else:
print(age)
python内置异常结构
BaseException
+-- SystemExit
+-- KeyboardInterrupt
+-- GeneratorExit
+-- Exception
+-- StopIteration
+-- StopAsyncIteration
+-- ArithmeticError
| +-- FloatingPointError
| +-- OverflowError
| +-- ZeroDivisionError
+-- AssertionError
+-- AttributeError
+-- BufferError
+-- EOFError
+-- ImportError
| +-- ModuleNotFoundError
+-- LookupError
| +-- IndexError
| +-- KeyError
+-- MemoryError
+-- NameError
| +-- UnboundLocalError
+-- OSError
| +-- BlockingIOError
| +-- ChildProcessError
| +-- ConnectionError
| | +-- BrokenPipeError
| | +-- ConnectionAbortedError
| | +-- ConnectionRefusedError
| | +-- ConnectionResetError
| +-- FileExistsError
| +-- FileNotFoundError
| +-- InterruptedError
| +-- IsADirectoryError
| +-- NotADirectoryError
| +-- PermissionError
| +-- ProcessLookupError
| +-- TimeoutError
+-- ReferenceError
+-- RuntimeError
| +-- NotImplementedError
| +-- RecursionError
+-- SyntaxError
| +-- IndentationError
| +-- TabError
+-- SystemError
+-- TypeError
+-- ValueError
| +-- UnicodeError
| +-- UnicodeDecodeError
| +-- UnicodeEncodeError
| +-- UnicodeTranslateError
+-- Warning
+-- DeprecationWarning
+-- PendingDeprecationWarning
+-- RuntimeWarning
+-- SyntaxWarning
+-- UserWarning
+-- FutureWarning
+-- ImportWarning
+-- UnicodeWarning
+-- BytesWarning
+-- ResourceWarning