How would you describe what is going on in the following code?
my_module.py :
my_dict = { "key": "default value" }
my_str = "default"
Python interpreter:
>>> from my_module import my_dict, my_str
>>> import my_module
>>>
>>> assert my_dict == { "key": "default value" }
>>> assert my_module.my_dict == { "key": "default value" }
>>> assert my_str == "default string"
>>> assert my_module.my_str == "default string"
>>>
>>> my_dict["key"] = "new value"
>>> my_str = "new string"
>>>
>>> assert my_dict == { "key": "new value" }
>>> assert my_module.my_dict == { "key": "new value" } # why did this change?
>>> assert my_str == "new string"
>>> assert my_module.my_str == "default string" # why didn't this change?
>>>
>>> my_module.my_dict["key"] = "new value 2"
>>> my_module.my_str = "new string 2"
>>>
>>> assert my_dict == { "key": "new value 2" } # why did this change?
>>> assert my_module.my_dict == { "key": "new value 2" }
>>> assert my_str == "new string" # why didn't this change?
>>> assert my_module.my_str == "new string 2"
>>>
>>> my_dict = { "new_dict key" : "new_dict value" }
>>> assert my_dict == { "new_dict key": "new_dict value" }
>>> assert my_module.my_dict == { "key": "new value 2" } # why didn't this change?
my_module.my_str
refers to the my_str
object in the my_module
namespace, and modifying my_module.my_str
modifies that object.
from my_module import my_str
creates a my_str
object in the local namespace, copied from the my_module.my_str
object. Modifying my_str
modifies the object in the local namespace, but does not modify the my_module.my_str
object.
my_dict
is a reference in the local namespace to my_module.my_dict
. Because it's a reference to a mutable object (a dictionary), changes made to my_dict
affect my_module.my_dict
and vice versa.
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