Two instances of class share same vairable in Python
So this is very wierd. The code below creates 2 instances of MyClass. One would expect that each has its own copy of the private variable __x which is a dictionary. However, my_class2 updates the value of __x in my_class1 which should not happen in my opinion?
What am I missing?
class MyClass:
__x = dict()
def __init__(self, name, init_value):
self.__x[name] = init_value
def get_value(self):
return self.__x
if __name__ == '__main__':
my_class1 = MyClass("one", 1)
print("my_class1: {}".format(my_class1.get_value()))
my_class2 = MyClass("two", 2)
print("my_class2: {}".format(my_class2.get_value()))
print("my_class1: {}".format(my_class1.get_value()))
The code above leads to the following output:
my_class1: {'one': 1}
my_class2: {'one': 1, 'two': 2}
my_class1: {'one': 1, 'two': 2}
python-3.x class object
asked Nov 23 '18 at 12:57
PaulPaul
7611
add a comment |
So this is very wierd. The code below creates 2 instances of MyClass. One would expect that each has its own copy of the private variable __x which is a dictionary. However, my_class2 updates the value of __x in my_class1 which should not happen in my opinion?
What am I missing?
class MyClass:
__x = dict()
def __init__(self, name, init_value):
self.__x[name] = init_value
def get_value(self):
return self.__x
if __name__ == '__main__':
my_class1 = MyClass("one", 1)
print("my_class1: {}".format(my_class1.get_value()))
my_class2 = MyClass("two", 2)
print("my_class2: {}".format(my_class2.get_value()))
print("my_class1: {}".format(my_class1.get_value()))
The code above leads to the following output:
my_class1: {'one': 1}
my_class2: {'one': 1, 'two': 2}
my_class1: {'one': 1, 'two': 2}
python-3.x class object
asked Nov 23 '18 at 12:57
PaulPaul
7611
Yes. Of course. Missed that one. Instance variables are defined in functions.
– Paul
Nov 23 '18 at 13:04
add a comment |
So this is very wierd. The code below creates 2 instances of MyClass. One would expect that each has its own copy of the private variable __x which is a dictionary. However, my_class2 updates the value of __x in my_class1 which should not happen in my opinion?
What am I missing?
class MyClass:
__x = dict()
def __init__(self, name, init_value):
self.__x[name] = init_value
def get_value(self):
return self.__x
if __name__ == '__main__':
my_class1 = MyClass("one", 1)
print("my_class1: {}".format(my_class1.get_value()))
my_class2 = MyClass("two", 2)
print("my_class2: {}".format(my_class2.get_value()))
print("my_class1: {}".format(my_class1.get_value()))
The code above leads to the following output:
my_class1: {'one': 1}
my_class2: {'one': 1, 'two': 2}
my_class1: {'one': 1, 'two': 2}
python-3.x class object
asked Nov 23 '18 at 12:57
PaulPaul
7611
So this is very wierd. The code below creates 2 instances of MyClass. One would expect that each has its own copy of the private variable __x which is a dictionary. However, my_class2 updates the value of __x in my_class1 which should not happen in my opinion?
What am I missing?
class MyClass:
__x = dict()
def __init__(self, name, init_value):
self.__x[name] = init_value
def get_value(self):
return self.__x
if __name__ == '__main__':
my_class1 = MyClass("one", 1)
print("my_class1: {}".format(my_class1.get_value()))
my_class2 = MyClass("two", 2)
print("my_class2: {}".format(my_class2.get_value()))
print("my_class1: {}".format(my_class1.get_value()))
The code above leads to the following output:
my_class1: {'one': 1}
my_class2: {'one': 1, 'two': 2}
my_class1: {'one': 1, 'two': 2}
python-3.x class object
python-3.x class object
asked Nov 23 '18 at 12:57
PaulPaul
7611
asked Nov 23 '18 at 12:57
PaulPaul
7611
asked Nov 23 '18 at 12:57
PaulPaul
7611
asked Nov 23 '18 at 12:57
PaulPaul
7611
asked Nov 23 '18 at 12:57
PaulPaul
7611
7611
Yes. Of course. Missed that one. Instance variables are defined in functions.
– Paul
Nov 23 '18 at 13:04
add a comment |
Yes. Of course. Missed that one. Instance variables are defined in functions.
– Paul
Nov 23 '18 at 13:04
Yes. Of course. Missed that one. Instance variables are defined in functions.
– Paul
Nov 23 '18 at 13:04
Yes. Of course. Missed that one. Instance variables are defined in functions.
– Paul
Nov 23 '18 at 13:04
add a comment |
2 Answers
2
active
oldest
votes
You have to declare __x inside the __init__ function, like this:
class MyClass:
def __init__(self, name, init_value):
self.__x = dict()
self.__x[name] = init_value
def get_value(self):
return self.__x
answered Nov 23 '18 at 13:04
user9849588user9849588
45317
Yes, I got that just after I posted. Thanks.
– Paul
Nov 23 '18 at 13:05
add a comment |
In your case, the way you were defining __x - it was a class variable - i.e. a variable that is shared by all instances of this class.
You can see this if you run a dir on your instances:
dir(my_class1)
['_MyClass__x', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'get_value']
Note the first entry - it is same above and below.
dir(my_class2)
['_MyClass__x', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'get_value']
answered Nov 23 '18 at 13:16
MortzMortz
628417
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
You have to declare __x inside the __init__ function, like this:
class MyClass:
def __init__(self, name, init_value):
self.__x = dict()
self.__x[name] = init_value
def get_value(self):
return self.__x
answered Nov 23 '18 at 13:04
user9849588user9849588
45317
Yes, I got that just after I posted. Thanks.
– Paul
Nov 23 '18 at 13:05
add a comment |
You have to declare __x inside the __init__ function, like this:
class MyClass:
def __init__(self, name, init_value):
self.__x = dict()
self.__x[name] = init_value
def get_value(self):
return self.__x
answered Nov 23 '18 at 13:04
user9849588user9849588
45317
Yes, I got that just after I posted. Thanks.
– Paul
Nov 23 '18 at 13:05
add a comment |
You have to declare __x inside the __init__ function, like this:
class MyClass:
def __init__(self, name, init_value):
self.__x = dict()
self.__x[name] = init_value
def get_value(self):
return self.__x
answered Nov 23 '18 at 13:04
user9849588user9849588
45317
You have to declare __x inside the __init__ function, like this:
class MyClass:
def __init__(self, name, init_value):
self.__x = dict()
self.__x[name] = init_value
def get_value(self):
return self.__x
answered Nov 23 '18 at 13:04
user9849588user9849588
45317
answered Nov 23 '18 at 13:04
user9849588user9849588
45317
answered Nov 23 '18 at 13:04
user9849588user9849588
45317
answered Nov 23 '18 at 13:04
user9849588user9849588
45317
45317
Yes, I got that just after I posted. Thanks.
– Paul
Nov 23 '18 at 13:05
add a comment |
Yes, I got that just after I posted. Thanks.
– Paul
Nov 23 '18 at 13:05
Yes, I got that just after I posted. Thanks.
– Paul
Nov 23 '18 at 13:05
Yes, I got that just after I posted. Thanks.
– Paul
Nov 23 '18 at 13:05
add a comment |
In your case, the way you were defining __x - it was a class variable - i.e. a variable that is shared by all instances of this class.
You can see this if you run a dir on your instances:
dir(my_class1)
['_MyClass__x', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'get_value']
Note the first entry - it is same above and below.
dir(my_class2)
['_MyClass__x', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'get_value']
answered Nov 23 '18 at 13:16
MortzMortz
628417
add a comment |
In your case, the way you were defining __x - it was a class variable - i.e. a variable that is shared by all instances of this class.
You can see this if you run a dir on your instances:
dir(my_class1)
['_MyClass__x', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'get_value']
Note the first entry - it is same above and below.
dir(my_class2)
['_MyClass__x', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'get_value']
answered Nov 23 '18 at 13:16
MortzMortz
628417
add a comment |
In your case, the way you were defining __x - it was a class variable - i.e. a variable that is shared by all instances of this class.
You can see this if you run a dir on your instances:
dir(my_class1)
['_MyClass__x', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'get_value']
Note the first entry - it is same above and below.
dir(my_class2)
['_MyClass__x', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'get_value']
answered Nov 23 '18 at 13:16
MortzMortz
628417
In your case, the way you were defining __x - it was a class variable - i.e. a variable that is shared by all instances of this class.
You can see this if you run a dir on your instances:
dir(my_class1)
['_MyClass__x', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'get_value']
Note the first entry - it is same above and below.
dir(my_class2)
['_MyClass__x', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'get_value']
answered Nov 23 '18 at 13:16
MortzMortz
628417
answered Nov 23 '18 at 13:16
MortzMortz
628417
answered Nov 23 '18 at 13:16
MortzMortz
628417
answered Nov 23 '18 at 13:16
MortzMortz
628417
628417
add a comment |
add a comment |
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Yes. Of course. Missed that one. Instance variables are defined in functions.
– Paul
Nov 23 '18 at 13:04