python appends to all dictionaries

Question

I am using dictoinaries inside of dictionaries. Looping through a pandas dataframe, the value of the action row always matches one of the keys in the dictionary, and based on that some other values from that row are appended to a list in that dictionary. For some reason, however, the values are appended to all lists in the other dictionaries

    general_form = {
        "Percentage": np.nan, "DayPercentage": np.nan, "sample_size": np.nan, "Percentages": [], "DayPercentages": []
    }
    #get all possible action types
    action_types = self.df['Action Type'].tolist()
    action_types = list(set(action_types))

    #give every action type its own dictionary within the main dictionary
    sheetstats = {}
    for action in action_types:
        sheetstats[action] = general_form

    #push the percentage in the list inside the dictionary specified in 
    #action
    for index, row in self.df.iterrows():
        percentage = row['Percentage']
        daypercentage = row['DayPercentage']
        action = row['Action Type']
        sheetstats[action]['Percentages'].append(percentage)
        sheetstats[action]["DayPercentages"].append(daypercentage)

This will make all of the percentages identical in all dictionaries inside sheetstats. Why?

Answer 1

sheetstats[action] = general_form 

Is basically putting the same dictionary in every key slot, you can think of this as each key pointing back to general_form

What you can do is make a copy of general_form:

for action in action_types:
    sheetstats[action] = dict(general_form)

The proper way to copy data structure is to use the module copy and it's deepcopy function which will copy deep structures (such as classes):

import copy
for action in action_types:
    sheetstats[action] = copy.deepcopy(general_form)

Answer 2

You are assigning general_form on every iteration.

Could it be you want to assign the value from action_types?

sheetstats[action] = action_types[action] ?

general_form = {
        "Percentage": np.nan, "DayPercentage": np.nan, "sample_size": np.nan, "Percentages": [], "DayPercentages": []
    }
    #get all possible action types
    action_types = self.df['Action Type'].tolist()
    action_types = list(set(action_types))

    #give every action type its own dictionary within the main dictionary
    sheetstats = {}
    for action in action_types:
        sheetstats[action] = action_types[action]

    #push the percentage in the list inside the dictionary specified in 
    #action
    for index, row in self.df.iterrows():
        percentage = row['Percentage']
        daypercentage = row['DayPercentage']
        action = row['Action Type']
        sheetstats[action]['Percentages'].append(percentage)
        sheetstats[action]["DayPercentages"].append(daypercentage)