[Introduction to Udemy Python3 + Application] 65. Exception handling

** * This article is from Udemy "[Introduction to Python3 taught by active Silicon Valley engineers + application + American Silicon Valley style code style](https://www.udemy.com/course/python-beginner/" Introduction to Python3 taught by active Silicon Valley engineers + application + American Silicon Valley style code style ")" It is a class notebook for myself after taking the course of. It is open to the public with permission from the instructor Jun Sakai. ** **

■ Exception handling

◆ Basic

l = [0, 1, 2]
i = 5

try:
    print(l[i])
except:
    print('Error!')

result


Error!

If you try to do what you write in try: and it fails due to some error The processing in ʻexcept:` is executed.

◆ Specifying the type of error

l = [0, 1, 2]
del l

try:
    print(l)
except IndexError as ex:
    print('Error massage: {}'.format(ex))
except NameError as ex:
    print('Error massage: {}'.format(ex))

result


Error massage: name 'l' is not defined

If it is ʻIndexError, this process, You can also specify the type of error, such as this process if it is NameError`.

◆finally:

l = [0, 1, 2]
i = 5

try:
    print(l[i])
except:
    print('Error!')
finally:
    print('clean up')

result


Error!
clean up

The process written in finally: is always executed regardless of whether try succeeds or except.

l = [0, 1, 2]
i = 5

try:
    print(l[i])
finally:
    print('clean up')

result


clean up
Traceback (most recent call last):
  File "/~~~", line 5, in <module>
    print(l[i])
IndexError: list index out of range

Therefore, even if an error actually occurs, the processing in finally will be executed first, and then the program will stop with an error.

◆else:

l = [0, 1, 2]

try:
    print(l[0])
except:
    print('Error!')
else:
    print('done')

result


0
done

With ʻelse:, the processing in ʻelse: is executed only if the processing in try: is successful.

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