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Complete Python exception handling in ten minutes

2022-06-24 08:00:03Python researcher

exception handling :

Capture exception , Simple catch exception syntax , In program development , You can try to add try To catch exceptions

try:
     Code to try to execute 
except:
   Wrong handling 

try Try Fill in the password you want to try below , Code that is not sure whether it will execute properly

except If not , Fill in the failure code below

Example : Simple exception capture drill – User is required to enter an integer

try:
    # Not sure what code you're trying to execute 
    # Prompt user for a number 
    num = int(input(" Please enter a number :"))
except:
    print(" Please enter a correct number !")
print("-"*50)

Error type capture :

When the program is executed , You may encounter different types of , And you need to target different types of exceptions , Respond differently , At this point, you need to specify the error type

try:
    # Code to try to execute 
    pass
except  Wrong type 1:
    # For the type of error 1, Corresponding code handling 
    pass
except( Wrong type 2, Wrong type 3):
    # For the type of error 2  and 3  Corresponding code handling 
    pass
except Exception as result:
    print(" Unknown error  %s" %result)

Sample requirements :

Prompt the user to enter an integer

Use 8 Divide by the integer entered by the user and output

while True:
    try:
        #  Prompt the user to enter an integer 
        num = int(input(" Enter an integer :"))
        #  If the input is not an integer, an error will be reported , Input 0 It's also a mistake , Here we need to catch exceptions   The first word with wrong assignment is treated as a keyword 
        result = 8 / num
        print(result)
    except ZeroDivisionError:
        print(" Mathematical error ")
    except ValueError:
        print(" Please enter a number ")

Catch unknown error :

except Exception as result:
    print(" Unknown error  %s" %result)

Unknown errors can be output to the console , Instead of reporting an error and crashing Exception keyword

try:
    #  Prompt the user to enter an integer 
    num = int(input(" Enter an integer :"))
    #  If the input is not an integer, an error will be reported , Input 0 It's also a mistake , Here we need to catch exceptions   The first word with wrong assignment is treated as a keyword 
    result = 8 / num
    print(result)
except ValueError:
    print(" Please enter a number ")
except Exception as result:
    print(" Unknown error %s"%result)

Complete syntax for exception capture :

try:
    # Code to try to execute 
    pass
except  Wrong type 1 The first keyword of :
  # For the type of error 1 Corresponding code handling 
    pass
except  Wrong type 2 First keyword of :
    # For the type of error 2 Corresponding code processing of 
    pass
except ( Wrong type 3, Wrong type 4):
    # For the type of error 3,4 Corresponding code processing of 
    pass
except Exception as result:
    # Print error messages 
    print(result)
else:
    # Code that will execute without exception 
    pass
finally:
    # No matter whether there is any abnormality , Code that will execute 
    print(" Whether or not there are exceptions , Code that will execute ")

Sample code :

try:
    #  Prompt the user to enter an integer 
    num = int(input(" Enter an integer :"))
    #  If the input is not an integer, an error will be reported , Input 0 It's also a mistake , Here we need to catch exceptions   The first word with wrong assignment is treated as a keyword 
    result = 8 / num
    print(result)
except ValueError:
    print(" Please enter a number ")
except Exception as result:
    print(" Unknown error %s" % result)
else:
    print(" Try to succeed !")
finally:
    print(" Code that executes regardless of whether an error occurs ")
print("==="*20)

The transmission of exceptions :

Function as / When an exception occurs in method execution , The exception is passed to the function / The caller of the method

If passed to the main program , Still no exception handling , The program will be terminated

So , You only need to do an exception handling in the main program to complete the exception handling of the code

Sample code :

def demo1():
    return int(input(" Input integer :"))
def demo2():
    return demo1()
# Take advantage of the transitivity of exceptions , Catch exception in main program 
try:
    print(demo2())
except Exception as result:
    print(" The program appears %s error "%(result))

Throw out raise abnormal :

Actively throw an exception

python One is provided in Exception Exception class

At development time , If you meet the needs of a particular business , Hope to throw an exception , Sure

Create a Exception The object of

Use raise Keyword throws an exception object

Demand case :

Definition input_password function , Prompt user for password

If the user enters the length <8, Throw an exception

If the user enters the length >=8 Return the password entered

def input_password():
    #1. Prompt user for password 
    result =input(" Please input a password ")
    #2. Determine password length  >=8 , Return the password entered by the user 
    if len(result) >=8:
        return result
    #3. If <8  Actively throw an exception 
    print(" Actively throw an exception !")
    #1> Create exception object  - You can use the error message string as an argument 
    ex =Exception(" Insufficient password length !")
    #2>  Actively throw an exception 
    raise ex
# Prompt user for password 
try:
    print(input_password())
except Exception as result:
    print(result)

The above is python All all exception handling , It's a little bit easier !

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