Don't panic when Python reports an error. These three keywords help you solve the problem!

Chen Python 2020-11-17 21:02:50
don panic python reports error.

There are bound to be errors in writing code , Error handling can be prepared for these errors in advance . Usually when something goes wrong , The script stops running , And with error handling , You can continue to run the script . So , We need to know the following three key words :

  • try: This is the code block to run , Errors may occur .
  • except: If in try Error in block , This code will be executed .
  • finally: No matter what mistakes , It's all code execution .

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Now? , Let's define a function “summation”, Add two numbers together . This function works properly .

>>> defsummation(num1,num2):

Next , We asked the user to enter one of the numbers , And run the function .

>>> num1 = 2
>>> num2 = input("Enter number: ")
Enter number: 3>>> summation(num1,num2)>>> print("Thisline will not be printed because of the error")
TypeError Traceback (most recent call last)
<ipython-input-6-2cc0289b921e> in <module>
----> 1 summation(num1,num2)
2 print("This line will notbe printed because of the error")
<ipython-input-1-970d26ae8592> in summation(num1, num2)
1 def summation(num1,num2):
----> 2 print(num1+num2)
TypeError: unsupported operand type(s) for +: int and str


“TypeError” The error occurred , Because we're trying to add numbers to strings . Please note that , When a mistake occurs , The later code is no longer executed . So we need to use the keywords mentioned above , Make sure that even if something goes wrong , The script still runs .

>> try:
summed = 2 + 3
print("Summation is not ofthe same type")Summation is not of the same type

You can see ,try Block error ,except Block code starts running , And print the statement . Next, join “else” block , To deal with situations where there are no mistakes .

>>> try:
summed = 2 + 3
print("Summation is not ofthe same type")
print("There was no errorand result is: ",summed)There was no error and result is: 5

Let's take another example . In this case , stay except We also indicate the type of error . If the error type is not indicated , All exceptions will be executed except block .

>>> try:
f = open( test , w )
f.write("This is a testfile")
except TypeError:
print("There is a typeerror")
except OSError:
print("There is an OSerror")
print("This will print evenif no error")This will print even if no error

Now? , Deliberately create a mistake , have a look except Whether the block is consistent with finally Let's work together !

>>> try:
f = open( test , r )
f.write("This is a testfile")
except TypeError:
print("There is a typeerror")
except OSError:
print("There is an OSerror")
print("This will print evenif no error")There is an OS error
This will print even if no error


本文为[Chen Python]所创,转载请带上原文链接,感谢

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