CODEWITHSUNDEEP
pythonpython-3.xclassdictionaryinitialization
Matt Ellis
Matt Ellis

Reputation: 162

Creating a new dictionary variable in a class python

If I create a class like below:

class Foo(object): 
     foo = {'useful_info': 'useful_info'}  
     def __init__(self, foo, bar): 
         self.foo['foo'] = foo 
         self.bar = bar

and I create an instances of it and print it's attributes as:

Foo1 = Foo('foo1', 'bar1')
print(Foo1.foo)
print(Foo1.bar)

I get the output:

Foo1 = Foo('foo1', 'bar1')
print(Foo1.foo)
print(Foo1.bar)

However, now if I create a new instance named Foo2 and print the attributes of both Foo1 and Foo2 as:

Foo2 = Foo('foo2', 'bar2')

print("Foo2.foo: ", Foo2.foo) 
print("Foo2.bar: ", Foo2.bar) 
print("Foo1.foo: ", Foo1.foo) 
print("Foo1.bar: ", Foo1.bar)

I get the output:

Foo2.foo:  {'foo': 'foo2'}
Foo2.bar:  bar2
Foo1.foo:  {'foo': 'foo2'}
Foo1.bar:  bar1

The string attributes bar have been set as I expect, but the dictionary foo has been updated for both instances of Foo.

I can get round this by declaring the dict foo in the init magic method as:

class Foo(object): 
     def __init__(self, foo, bar): 
         self.foo = {'useful_info': 'useful_info'} 
         self.foo['foo'] = foo 
         self.bar = bar

but now the dictionary foo containing 'useful_info' isn't accessible until the init function is called i.e. if I use the line: Foo.foo I get an AttributeError.

Is there any way to create a new dictionary containing some 'useful_infomation' so that the useful info is accessible before the class is initialised and every new instance of a class has a different instance of this dictionary.

Upvotes: 0

Views: 48

Answers (2)

Cory Kramer
Cory Kramer

Reputation: 118011

You can make a copy.deepcopy of the dictionary within __init__ so each instance has a deep copy of the dictionary, instead of sharing the same foo dictionary object.

import copy

class Foo(object): 
    foo = {'useful_info': 'useful_info'}  
    def __init__(self, bar): 
        self.foo = copy.deepcopy(Foo.foo)
        self.bar = bar

Upvotes: 1

juanpa.arrivillaga
juanpa.arrivillaga

Reputation: 96286

Just combine both:

class Foo:
    foo = {'useful_info': 'useful_info'}
    def __init__(self, foo, bar):
        self.foo = {'useful_info': 'useful_info'}
        self.foo['foo'] = foo
        self.bar = bar

Upvotes: 1

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