Python exception handling

Typical exception

TypeError Example: TypeError: unsupported operand type (s) for /:'str' and'int' Error that occurs when trying to calculate the String type

ZeroDivisionError Example: ZeroDivisionError: division by zero Error that occurs when dividing by zero like 1/0

NameError Example: NameError: name'hoge' is not defined Error when using undefined variables

AttributeError Example: AttributeError: type object ‘list’ has no attribute ‘fuga’ Error when trying to access a non-existent attribute

Python exception handling rules

--try: Exception handling of enclosed code --ʻExcept : Block to be executed when an error-case exception occurs --ʻExcept: Block to execute when any exception occurs --ʻElse: Block to execute only if no exception occurs --finally`: Block to execute with or without an exception

try-except Used when you want to continue the process even if an error is derived from the executed process.


Num = [1,2,3]
n = 4

#Extract errors while continuing processing
try:
    print(Num[n])  
except:
    print('error')  #データがない場合、error

print('Continue processing')

#Output result
error
Continue processing

Other exception handling

If there are multiple exceptions, the processing is divided according to the type of exception.

Num = [1,2,3,4]
n = 5
n = 'String'   

try:
    print(Num[n])
except IndexError as ie:
    print('error contents: {}'.format(ie))
except NameError as ne:
    print(ne)
except Exception as ex:　#When an error other than IndexError and NameError occurs
    print('error contents: {}'.format(ex))

print('Exception occurred')

#Output result
error contents: list indices must be integers or slices, not str
Exception occurred

finaly Even if an error occurs, always execute the following processing in finaly

Num = [1,2,3,4]
n = 5
n = 'String'   

try:
    print(Num[n])
except IndexError as ie:
    print('error contents: {}'.format(ie))
except NameError as ne:
    print(ne)
except Exception as ex:　#When an error other than IndexError and NameError occurs
    print('error contents: {}'.format(ex))
finally:    #← Process that you definitely want to execute
    print('Must be executed')

print('Exception occurred')

#Output result
error contents: list indices must be integers or slices, not str
Must be executed
Exception occurred

raise and pass

Use raise if you want to intentionally raise an error

try:
    raise TypeError
except:
    print('Intentionally generate an error')