异常处理
2018-12-15 本文已影响1人
水之心
-
Exception：Python 内置的异常类 -
raise：抛出异常 -
try：尝试运行以下语句 -
except：在try语句之后，捕获某个异常，为空则捕获全部异常（很危险，难以 debug） -
else：在try语句之后，如果没有捕获异常，则执行 -
finally：在try语句之后，无论是否捕获异常，均执行
try:
print("Enter try.")
except:
print("Enter except.")
else:
print("Enter else.")
finally:
print("Enter finally.")
Enter try.
Enter else.
Enter finally.
try:
print("Enter try.")
1 / 0
except:
print("Enter except.")
else:
print("Enter else.")
finally:
print("Enter finally.")
Enter try.
Enter except.
Enter finally.
try:
print("Enter try.")
1 / 0
except ZeroDivisionError:
print("Enter except ZeroDivisionError.")
except ArithmeticError:
print("Enter except ArithmeticError.")
except:
print("Enter except.")
else:
print("Enter else.")
finally:
print("Enter finally.")
Enter try.
Enter except ZeroDivisionError.
Enter finally.
MODE = "DEBUG"
try:
print("Enter try.")
1 / 0
except:
print("Enter except.")
if MODE == "DEBUG":
raise
else:
print("Enter else.")
finally:
print("Enter finally.") # 先执行，再抛出异常
Enter try.
Enter except.
Enter finally.
---------------------------------------------------------------------------
ZeroDivisionError Traceback (most recent call last)
<ipython-input-4-9784fbc6b503> in <module>()
2 try:
3 print("Enter try.")
----> 4 1 / 0
5 except:
6 print("Enter except.")
ZeroDivisionError: division by zero
MODE = "WARN"
try:
print("Enter try.")
1 / 0
except Exception as e:
print("Enter except.")
if MODE == "DEBUG":
raise
elif MODE == "WARN":
print(e)
else:
print("Enter else.")
finally:
print("Enter finally.")
Enter try.
Enter except.
division by zero
Enter finally.
MODE = "WARN"
def main():
while True:
try:
print("Please input your Python 3 Expression.")
exp = input()
print("The result of your expression is", eval(exp))
except Exception as e:
if MODE == "DEBUG":
raise
elif MODE == "WARN":
print(e)
elif MODE == "STABLE":
print("Something wrong, please input again.")
else:
break
if __name__ == "__main__":
main()
Please input your Python 3 Expression.
1/0
division by zero
Please input your Python 3 Expression.
1=1
invalid syntax (<string>, line 1)
Please input your Python 3 Expression.
2**4
The result of your expression is 16
异常的传播
def f1():
try:
return 1 / 0
except Exception as e:
print("This is f1.")
print(e)
def f2():
try:
f1()
except Exception as e:
print("This is f2.")
print(e)
def f3():
try:
f2()
except Exception as e:
print("This is f3.")
print(e)
def main():
try:
f3()
except Exception as e:
print("This is main.")
print(e)
if __name__ == "__main__":
try:
main()
except Exception as e:
print("This is __main__.")
print(e)
This is f1.
division by zero
def f1():
try:
return 1 / 0
except Exception as e:
print("This is f1.")
print(e)
raise
def f2():
try:
f1()
except Exception as e:
print("This is f2.")
print(e)
def f3():
try:
f2()
except Exception as e:
print("This is f3.")
print(e)
def main():
try:
f3()
except Exception as e:
print("This is main.")
print(e)
if __name__ == "__main__":
try:
main()
except Exception as e:
print("This is __main__.")
print(e)
This is f1.
division by zero
This is f2.
division by zero
def f1():
try:
return 1 / 0
except Exception as e:
print("This is f1.")
print(e)
raise
def f2():
try:
f1()
except Exception as e:
print("This is f2.")
print(e)
raise
def f3():
try:
f2()
except Exception as e:
print("This is f3.")
print(e)
raise
def main():
try:
f3()
except Exception as e:
print("This is main.")
print(e)
raise
if __name__ == "__main__":
try:
main()
except Exception as e:
print("This is __main__.")
print(e)
This is f1.
division by zero
This is f2.
division by zero
This is f3.
division by zero
This is main.
division by zero
This is __main__.
division by zero
def f1():
try:
return 1 / 0
except Exception as e:
print("This is f1.")
print(e)
raise
def f2():
try:
f1()
except Exception as e:
print("This is f2.")
print(e)
raise
def f3():
try:
f2()
except Exception as e:
print("This is f3.")
print(e)
raise
def main():
try:
f3()
except Exception as e:
print("This is main.")
print(e)
raise
if __name__ == "__main__":
try:
main()
except Exception as e:
print("This is __main__.")
print(e)
raise
This is f1.
division by zero
This is f2.
division by zero
This is f3.
division by zero
This is main.
division by zero
This is __main__.
division by zero
---------------------------------------------------------------------------
ZeroDivisionError Traceback (most recent call last)
<ipython-input-10-19f0b6cf0b7a> in <module>()
37 if __name__ == "__main__":
38 try:
---> 39 main()
40 except Exception as e:
41 print("This is __main__.")
<ipython-input-10-19f0b6cf0b7a> in main()
28 def main():
29 try:
---> 30 f3()
31 except Exception as e:
32 print("This is main.")
<ipython-input-10-19f0b6cf0b7a> in f3()
19 def f3():
20 try:
---> 21 f2()
22 except Exception as e:
23 print("This is f3.")
<ipython-input-10-19f0b6cf0b7a> in f2()
10 def f2():
11 try:
---> 12 f1()
13 except Exception as e:
14 print("This is f2.")
<ipython-input-10-19f0b6cf0b7a> in f1()
1 def f1():
2 try:
----> 3 return 1 / 0
4 except Exception as e:
5 print("This is f1.")
ZeroDivisionError: division by zero
