Exception Handling 异常处理
exception - error
异常 - 错误
try... except...
try:
test a block of code for errors.
测试代码块中的错误。
except:
handle the error.
处理错误。
How they work
If try block raises an error, except block will be executed.
如果 try 块引发错误，则执行 except 块。
Example
try:
print(x) # x is not defined
except:
print("An exception occurred")
Multiple exceptions - 3 examples
Name error
# Print one message if the try block raises a NameError and another for other errors
try:
print(x) # name error
except NameError:
print("Variable x is not defined")
except:
print("Something else went wrong")
output: Variable x is not defined
Other errors
try:
x = 'a'
x = x + 1 # other error
except NameError:
print("Variable x is not defined")
except:
print("Something else went wrong")
Output: Something else went wrong
Sequence
try:
print(x) # name error
x = 'a'
x = x + 1 # other error
except NameError:
print("Variable x is not defined")
except:
print("Something else went wrong")
Output: Variable x is not defined
execute the code triggered by the first exception.
执行由第一个异常触发的代码。
Else
How it works
else executed this code if no errors were raised.
else 如果没有引起错误，则执行此代码.
Example
try:
print("Hello.") # the try block does not generate any error
except:
print("Something went wrong.")
else:
print("Nothing went wrong.")
Outout: Hello. Nothing went wrong.
Finally
finally:
execute code regardless if the try block raises an error or not.
无论 try 块是否引发错误，都执行代码。
Example
try:
print(x)
except:
print("Something went wrong.")
finally:
print("The 'try except' is finished.")
Output: Something went wrong. The 'try except' is finished.
Raise an exception
raise throws(raises) an exception.
raise + type of error/Exception ("text to print")
Example
# Raise a TypeError if x is not an integer:
x = "hello"
if not type(x) is int:
raise TypeError("Only integers are allowed")
Output:
Traceback (most recent call last):
File "demo_ref_keyword_raise2.py", line 4, in <module>
raise TypeError("Only integers are allowed")
TypeError: Only integers are allowed
References
Relative Information
use 'while True' to put it in a loop
'continue' means to repeat the loop
'break' means to exit the loop
