weird error with Python (2.7) default empty dictionary inside class

Question

In the code I'm working with I have a pretty simple class that looks like this:

class SampleClass:
    def __init__(self,name="Untitled",data={}):
         self.name = name
         self.data = data

Later on I have a function to update the name and data of this class:

def update_name(sample_class):
    new_name = raw_input(enter a name: )
    sample_class.name = new_name

def update_data(sample_class):
    key = raw_input(enter a key: )
    value = raw_input(enter a value: )
    sample_class.data[key] = value

For some reason when I use the update_data function, it adds to the self.data of every object of the class SampleClass. For example if I had:

sample_class_1 = SampleClass()
sample_class_2 = SampleClass()

, and I added a key-value pair to sample_class_1 with update_data(sample_class_1), it would add that key-value pair to sample_class_2 as well.

Even further, after using this function, if I create a brand new SampleClass with a new name, even then, the newly created self.data will not be an empty dictionary, and will contain the key-value pair just inserted into sample_class_1.

How can I modify this code so that I can add key-value pairs to one single self.data dictionary at a time?

Don't use `{}` as a default. Change it to `data=None` and then `self.data = data or {}` — tzaman, Feb 19 '16 at 22:19
That's because you used the "once and future" empty dictionary constant. Every time you use it, the data gets set to the primal empty dictionary: they all point to the same object. Use copy( {} ) to get individual versions. — Prune, Feb 19 '16 at 22:19

weird error with Python (2.7) default empty dictionary inside class

0 Answers0