Cara menggunakan python __init__ exception

Python telah menjadi bahasa berorientasi objek sejak bahasa Python sendiri dibuat. Untuk membuat dan menggunakan kelas dan objek pada Python benar-benar mudah. Pada tutorial ini Anda akan dibantu untuk menjadi ahli dalam penggunaan pemrograman berorientasi objek Python.

Jika Anda tidak memiliki pengalaman sebelumnya dengan pemrograman berorientasi objek (OOP), Anda mempelajarinya terlebih dahulu agar Anda dapat memahami konsep dasarnya.

Jika memang sudah mengerti konsep dasar OOP berikut ini adalah pengenalan dari Object-Oriented Programming (OOP) untuk membantu Anda.

Istilah Dalam OOP

Membuat Class Python

Statement class digunakan untuk membuat definisi kelas baru. Nama kelas segera mengikuti kelas kata kunci diikuti oleh titik dua sebagai berikut.

class ClassName: 'Optional class documentation string' class_suite

Dibawah ini adalah contoh cara membuat class dan penggunaanya :

class Employee:
'Common base class for all employees'
empCount = 0

def **init**(self, name, salary):
self.name = name
self.salary = salary
Employee.empCount += 1

def displayCount(self):
print "Total Employee %d" % Employee.empCount

def displayEmployee(self):
print "Name : ", self.name, ", Salary: ", self.salary

Membuat Instance Objects

Untuk membuat instances kelas, Anda memanggil class menggunakan nama class dan meneruskan argumen apa pun yang metode init terima.

This would create first object of Employee class
emp1 = Employee("Zara", 2000)
This would create second object of Employee class
emp2 = Employee("Manni", 5000)

Mengakses Atribut

Anda mengakses atribut objek menggunakan dot operator dengan objek. Variabel kelas akan diakses dengan menggunakan nama kelas sebagai berikut :

It is perfectly fine to raise an exception in __init__. You would then wrap the object initiation/creation call with try/except and react to the exception.

One potential odd result though is that __del__ is run anyway:

class Demo(object):
    def __init__(self, value):
        self.value=value
        if value==2:
            raise ValueError
    def __del__(self):
        print '__del__', self.value


d=Demo(1)     # successfully create an object here
d=22          # new int object labeled 'd'; old 'd' goes out of scope
              # '__del__ 1' is printed once a new name is put on old 'd'
              # since the object is deleted with no references 

Now try with the value

Demo(2)
Traceback (most recent call last):
  File "Untitled 3.py", line 11, in 
    Demo(2)           
  File "Untitled 3.py", line 5, in __init__
    raise ValueError
  ValueError
 __del__ 2 # But note that `__del__` is still run.

Demo(2)
Traceback (most recent call last):
  File "Untitled 3.py", line 11, in 
    Demo(2)           
  File "Untitled 3.py", line 5, in __init__
    raise ValueError
  ValueError
 __del__ 2 # But note that `__del__` is still run.

The creation of the object with value

Demo(2)
Traceback (most recent call last):
  File "Untitled 3.py", line 11, in 
    Demo(2)           
  File "Untitled 3.py", line 5, in __init__
    raise ValueError
  ValueError
 __del__ 2 # But note that `__del__` is still run.

Demo(2)
Traceback (most recent call last):
  File "Untitled 3.py", line 11, in 
    Demo(2)           
  File "Untitled 3.py", line 5, in __init__
    raise ValueError
  ValueError
 __del__ 2 # But note that `__del__` is still run.

Keep in mind that if you raise an exception during __init__ your object will not get a name. (It will, however, be created and destroyed. Since __del__ is paired with

Demo(2)
Traceback (most recent call last):
  File "Untitled 3.py", line 11, in 
    Demo(2)           
  File "Untitled 3.py", line 5, in __init__
    raise ValueError
  ValueError
 __del__ 2 # But note that `__del__` is still run.

ie, just like this does not create

Demo(2)
Traceback (most recent call last):
  File "Untitled 3.py", line 11, in 
    Demo(2)           
  File "Untitled 3.py", line 5, in __init__
    raise ValueError
  ValueError
 __del__ 2 # But note that `__del__` is still run.

>>> x=1/0
Traceback (most recent call last):
  File "", line 1, in 
ZeroDivisionError: integer division or modulo by zero
>>> x
Traceback (most recent call last):
  File "", line 1, in 
NameError: name 'x' is not defined

Potential sneakier:

>>> x='Old X'
>>> x=1/0
Traceback (most recent call last):
  File "", line 1, in 
ZeroDivisionError: division by zero
>>> x
'Old X'

Same thing if you catch an exception of __init__:

try:
    o=Demo(2)
except ValueError:
    print o          # name error -- 'o' never gets bound to the object...
                     # Worst still -- 'o' is its OLD value!

So don't try to refer to the incomplete object

Demo(2)
Traceback (most recent call last):
  File "Untitled 3.py", line 11, in 
    Demo(2)           
  File "Untitled 3.py", line 5, in __init__
    raise ValueError
  ValueError
 __del__ 2 # But note that `__del__` is still run.

>>> x=1/0
Traceback (most recent call last):
  File "", line 1, in 
ZeroDivisionError: integer division or modulo by zero
>>> x
Traceback (most recent call last):
  File "", line 1, in 
NameError: name 'x' is not defined

Demo(2)
Traceback (most recent call last):
  File "Untitled 3.py", line 11, in 
    Demo(2)           
  File "Untitled 3.py", line 5, in __init__
    raise ValueError
  ValueError
 __del__ 2 # But note that `__del__` is still run.

>>> x=1/0
Traceback (most recent call last):
  File "", line 1, in 
ZeroDivisionError: integer division or modulo by zero
>>> x
Traceback (most recent call last):
  File "", line 1, in 
NameError: name 'x' is not defined

So wrapping up (thanks to Steve Jessop for the idea), you can wrap the creation of the object and catch the exception. Just figure out how to react appropriately to the OS error you are looking at.

Apa itu exception pada Python?

Apa itu init pada Python?

Di dalam statement try apa arti dari except?

Apa yang dimaksud dengan modul pada Python?