I have read the below StackOverflow questions and my situation is similar but (I think) different:
My class creates what is meant to be an instance-level dictionary object. However, my constructor function provides a default value for that object. When I try to make an instance of my class with the default value, it suddenly behaves like it was class-level.
class store_a_dict:
def __init__(self,dict_in={"A":0}):
self.dict = dict_in
def increment(self):
self.dict["A"] += 1
def print_me(self):
print(self.dict)
test1 = store_a_dict({"A":3})
print("Initialised test1. Now test1 contains:")
test1.print_me()
test2 = store_a_dict()
print("Initialised test2 using default input. Now test2 contains:")
test2.print_me()
test2.increment()
print("Incremented test2. Now test2 contains:")
test2.print_me()
test3 = store_a_dict()
print("Initialised test3 using default input. Now test3 contains:")
test3.print_me()
print("We haven't touched test1, and it still contains:")
test1.print_me()
The code output is below. My expectation was that test3 should contain {'A': 0} after I initialised it using store_a_dict() with no inputs.
Initialised test1. Now test1 contains:
{'A': 3}
Initialised test2 using default input. Now test2 contains:
{'A': 0}
Incremented test2. Now test2 contains:
{'A': 1}
Initialised test3 using default input. Now test3 contains:
{'A': 1}
We haven't touched test1, and it still contains:
{'A': 3}
It seems like the obvious workaround is to change line 3 of my code to read self.dict = dict_in.copy(), but I want to understand why it works this way. Why is it perfectly happy to take in a value for dict_in when one is provided as part of a call to the class, and have it be isolated to the instance, but when I try to use the default value it suddenly seems to become a class-level object? Please help me understand this more deeply so I can avoid similar mistakes.
