Why do we need __init__ to initialize a python class










4















I'm pretty new to OOP and I need some help understanding the need for a constructor in a python class.



I understand init is used to initialize class variables like below:



class myClass():
def __init__ (self):
self.x = 3
print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)


Output:



object created
3
6


but, I could also just do,



class myClass():
x = 3
print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)


which prints out the same result.



Could you please explain why we need a constructor or give me an example of a case when the above method will not work?










share|improve this question






















  • You can read about class members vs instance members in python. This should improve your understandings.

    – florin
    Nov 15 '18 at 11:33











  • You can pass arguments to the class object and assign those values to class members in the constructor.

    – Nitin Pawar
    Nov 15 '18 at 11:34






  • 2





    Why do we use __init__ in Python classes?

    – Johnny Mopp
    Nov 15 '18 at 11:36















4















I'm pretty new to OOP and I need some help understanding the need for a constructor in a python class.



I understand init is used to initialize class variables like below:



class myClass():
def __init__ (self):
self.x = 3
print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)


Output:



object created
3
6


but, I could also just do,



class myClass():
x = 3
print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)


which prints out the same result.



Could you please explain why we need a constructor or give me an example of a case when the above method will not work?










share|improve this question






















  • You can read about class members vs instance members in python. This should improve your understandings.

    – florin
    Nov 15 '18 at 11:33











  • You can pass arguments to the class object and assign those values to class members in the constructor.

    – Nitin Pawar
    Nov 15 '18 at 11:34






  • 2





    Why do we use __init__ in Python classes?

    – Johnny Mopp
    Nov 15 '18 at 11:36













4












4








4








I'm pretty new to OOP and I need some help understanding the need for a constructor in a python class.



I understand init is used to initialize class variables like below:



class myClass():
def __init__ (self):
self.x = 3
print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)


Output:



object created
3
6


but, I could also just do,



class myClass():
x = 3
print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)


which prints out the same result.



Could you please explain why we need a constructor or give me an example of a case when the above method will not work?










share|improve this question














I'm pretty new to OOP and I need some help understanding the need for a constructor in a python class.



I understand init is used to initialize class variables like below:



class myClass():
def __init__ (self):
self.x = 3
print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)


Output:



object created
3
6


but, I could also just do,



class myClass():
x = 3
print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)


which prints out the same result.



Could you please explain why we need a constructor or give me an example of a case when the above method will not work?







python constructor init






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Nov 15 '18 at 11:29









DiletanteDiletante

10418




10418












  • You can read about class members vs instance members in python. This should improve your understandings.

    – florin
    Nov 15 '18 at 11:33











  • You can pass arguments to the class object and assign those values to class members in the constructor.

    – Nitin Pawar
    Nov 15 '18 at 11:34






  • 2





    Why do we use __init__ in Python classes?

    – Johnny Mopp
    Nov 15 '18 at 11:36

















  • You can read about class members vs instance members in python. This should improve your understandings.

    – florin
    Nov 15 '18 at 11:33











  • You can pass arguments to the class object and assign those values to class members in the constructor.

    – Nitin Pawar
    Nov 15 '18 at 11:34






  • 2





    Why do we use __init__ in Python classes?

    – Johnny Mopp
    Nov 15 '18 at 11:36
















You can read about class members vs instance members in python. This should improve your understandings.

– florin
Nov 15 '18 at 11:33





You can read about class members vs instance members in python. This should improve your understandings.

– florin
Nov 15 '18 at 11:33













You can pass arguments to the class object and assign those values to class members in the constructor.

– Nitin Pawar
Nov 15 '18 at 11:34





You can pass arguments to the class object and assign those values to class members in the constructor.

– Nitin Pawar
Nov 15 '18 at 11:34




2




2





Why do we use __init__ in Python classes?

– Johnny Mopp
Nov 15 '18 at 11:36





Why do we use __init__ in Python classes?

– Johnny Mopp
Nov 15 '18 at 11:36












2 Answers
2






active

oldest

votes


















4














Citation: But I can also do



class myClass():
x = 3
print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)


No you cannot. There is a fundamental difference once you want to create two or more objects of this same class. Maybe this behaviour becomes clearer like this



class MyClass:
x = 3
print("Created!")

a = MyClass() # Will output "Created!"
a = MyClass() # Will output nothing since the class already exists!


In principal you need __init__ in order to write that code that needs to get executed for every new object whenever this object gets initialized / created - not just once when the class is read in.






share|improve this answer


















  • 1





    Thank you, this helped my understanding!

    – Diletante
    Nov 15 '18 at 11:44


















2














__init__ is used to initialize the state of multiple instances of a class where each instance's state is decoupled from each other, whereas your second example, without __init__ initializes an attribute that is shared among all instances of a class.






share|improve this answer























  • Okay, my understanding became clearer.. Thank you :)

    – Diletante
    Nov 15 '18 at 11:45










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2 Answers
2






active

oldest

votes








2 Answers
2






active

oldest

votes









active

oldest

votes






active

oldest

votes









4














Citation: But I can also do



class myClass():
x = 3
print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)


No you cannot. There is a fundamental difference once you want to create two or more objects of this same class. Maybe this behaviour becomes clearer like this



class MyClass:
x = 3
print("Created!")

a = MyClass() # Will output "Created!"
a = MyClass() # Will output nothing since the class already exists!


In principal you need __init__ in order to write that code that needs to get executed for every new object whenever this object gets initialized / created - not just once when the class is read in.






share|improve this answer


















  • 1





    Thank you, this helped my understanding!

    – Diletante
    Nov 15 '18 at 11:44















4














Citation: But I can also do



class myClass():
x = 3
print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)


No you cannot. There is a fundamental difference once you want to create two or more objects of this same class. Maybe this behaviour becomes clearer like this



class MyClass:
x = 3
print("Created!")

a = MyClass() # Will output "Created!"
a = MyClass() # Will output nothing since the class already exists!


In principal you need __init__ in order to write that code that needs to get executed for every new object whenever this object gets initialized / created - not just once when the class is read in.






share|improve this answer


















  • 1





    Thank you, this helped my understanding!

    – Diletante
    Nov 15 '18 at 11:44













4












4








4







Citation: But I can also do



class myClass():
x = 3
print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)


No you cannot. There is a fundamental difference once you want to create two or more objects of this same class. Maybe this behaviour becomes clearer like this



class MyClass:
x = 3
print("Created!")

a = MyClass() # Will output "Created!"
a = MyClass() # Will output nothing since the class already exists!


In principal you need __init__ in order to write that code that needs to get executed for every new object whenever this object gets initialized / created - not just once when the class is read in.






share|improve this answer













Citation: But I can also do



class myClass():
x = 3
print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)


No you cannot. There is a fundamental difference once you want to create two or more objects of this same class. Maybe this behaviour becomes clearer like this



class MyClass:
x = 3
print("Created!")

a = MyClass() # Will output "Created!"
a = MyClass() # Will output nothing since the class already exists!


In principal you need __init__ in order to write that code that needs to get executed for every new object whenever this object gets initialized / created - not just once when the class is read in.







share|improve this answer












share|improve this answer



share|improve this answer










answered Nov 15 '18 at 11:39









quantquant

1,60211527




1,60211527







  • 1





    Thank you, this helped my understanding!

    – Diletante
    Nov 15 '18 at 11:44












  • 1





    Thank you, this helped my understanding!

    – Diletante
    Nov 15 '18 at 11:44







1




1





Thank you, this helped my understanding!

– Diletante
Nov 15 '18 at 11:44





Thank you, this helped my understanding!

– Diletante
Nov 15 '18 at 11:44













2














__init__ is used to initialize the state of multiple instances of a class where each instance's state is decoupled from each other, whereas your second example, without __init__ initializes an attribute that is shared among all instances of a class.






share|improve this answer























  • Okay, my understanding became clearer.. Thank you :)

    – Diletante
    Nov 15 '18 at 11:45















2














__init__ is used to initialize the state of multiple instances of a class where each instance's state is decoupled from each other, whereas your second example, without __init__ initializes an attribute that is shared among all instances of a class.






share|improve this answer























  • Okay, my understanding became clearer.. Thank you :)

    – Diletante
    Nov 15 '18 at 11:45













2












2








2







__init__ is used to initialize the state of multiple instances of a class where each instance's state is decoupled from each other, whereas your second example, without __init__ initializes an attribute that is shared among all instances of a class.






share|improve this answer













__init__ is used to initialize the state of multiple instances of a class where each instance's state is decoupled from each other, whereas your second example, without __init__ initializes an attribute that is shared among all instances of a class.







share|improve this answer












share|improve this answer



share|improve this answer










answered Nov 15 '18 at 11:42









solstice333solstice333

1,2331215




1,2331215












  • Okay, my understanding became clearer.. Thank you :)

    – Diletante
    Nov 15 '18 at 11:45

















  • Okay, my understanding became clearer.. Thank you :)

    – Diletante
    Nov 15 '18 at 11:45
















Okay, my understanding became clearer.. Thank you :)

– Diletante
Nov 15 '18 at 11:45





Okay, my understanding became clearer.. Thank you :)

– Diletante
Nov 15 '18 at 11:45

















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