如何维护现有字典python的顺序

Question

I created a dictionary, and later I'd like in insert it's values to a list. I know that lists keep their order, but I think that dictionaries are not. I know there is OrderedDict, but from what I understand it keeps the order upon addition to the dictionary. Here, I have already the complete dictionary, without adding to it.

I'm using python 3.6

My script is:

dirs_dictionary = {"user_dir_treatment":"/home/dataset_1/treatment",
                           "user_dir_control":"/home/dataset_1/control"}

empty_list = []

for key, value in dirs_dictionary.items()):
    empty_list.append(dirs_dictionary[key])

So eventually, I'd like that the list will contain the values in the same order as they are in the dictionary, meaning that the first item in the list is "/home/dataset_1/treatment" , and the second is "/home/dataset_1/control" .

How do I maintain the order of my dictionary?

Answer 1

In Python 3.6, dictionaries are ordered internally, but this is considered an implementation detail which should not be relied upon.

In Python 3.7, dictionaries are ordered.

Therefore, you have 2 options:

Use the implementation detail at your risk

You can use list(d) to retrieve the keys of the dictionary maintaining insertion order.

dirs_dictionary = {"user_dir_treatment":"/home/dataset_1/treatment",
                   "user_dir_control":"/home/dataset_1/control"}

empty_list = list(dirs_dictionary)

print(empty_list)

# ['user_dir_treatment', 'user_dir_control']

Use OrderedDict

from collections import OrderedDict

dirs_dictionary = OrderedDict([("user_dir_treatment", "/home/dataset_1/treatment"),
                               ("user_dir_control", "/home/dataset_1/control")]

empty_list = list(dirs_dictionary)

print(empty_list)

# ['user_dir_treatment', 'user_dir_control']