pythondictionarysetdefaultdictsetdefault

adding values to defaultdict set breaking on 128

Something always breaks once my address reaches value 128, and it stops putting the new value at the end of the nested dict. And instead starts ordering it from the beginning again. Why is it doing this?

result.setdefault(fan_definitions_name, set()).add(int(address))

live variable values

The structure of the data I'm looping through looks like this ->

list_address_of_selected_fans = [[101, 'standard fan definition1', 'JVEC-SP'],[102, 'standard fan definition1', 'JVEC-SP']]

EDIT: here is a runnable example where I provide the input. You can run this example directly (I'm using python 3.8.2)

list_address_of_selected_fans = [[101, 'standard fan definition1', 'JVEC-SP'],
                                 [102, 'standard fan definition1', 'JVEC-SP'],
                                 [103, 'standard fan definition1', 'JVEC-SP'],
                                 [104, 'standard fan definition1', 'JVEC-SP'],
                                 [105, 'standard fan definition1', 'JVEC-SP'],
                                 [106, 'standard fan definition1', 'JVEC-SP'],
                                 [107, 'standard fan definition1', 'JVEC-SP'],
                                 [108, 'standard fan definition1', 'JVEC-SP'],
                                 [109, 'standard fan definition1', 'JVEC-SP'],
                                 [110, 'standard fan definition1', 'JVEC-SP'],
                                 [111, 'standard fan definition1', 'JVEC-SP'],
                                 [112, 'standard fan definition1', 'JVEC-SP'],
                                 [113, 'standard fan definition1', 'JVEC-SP'],
                                 [114, 'standard fan definition1', 'JVEC-SP'],
                                 [115, 'standard fan definition1', 'JVEC-SP'],
                                 [116, 'standard fan definition1', 'JVEC-SP'],
                                 [117, 'standard fan definition1', 'JVEC-SP'],
                                 [118, 'standard fan definition1', 'JVEC-SP'],
                                 [119, 'standard fan definition1', 'JVEC-SP'],
                                 [120, 'standard fan definition1', 'JVEC-SP'],
                                 [121, 'standard fan definition1', 'JVEC-SP'],
                                 [122, 'standard fan definition1', 'JVEC-SP'],
                                 [123, 'standard fan definition1', 'JVEC-SP'],
                                 [124, 'standard fan definition1', 'JVEC-SP'],
                                 [125, 'standard fan definition1', 'JVEC-SP'],
                                 [126, 'standard fan definition1', 'JVEC-SP'],
                                 [127, 'standard fan definition1', 'JVEC-SP'],
                                 [128, 'standard fan definition1', 'JVEC-SP'],
                                 [129, 'standard fan definition1', 'JVEC-SP'],
                                 [130, 'standard fan definition1', 'JVEC-SP'],
                                 [131, 'standard fan definition1', 'JVEC-SP'],
                                 [132, 'standard fan definition1', 'JVEC-SP'],
                                 [133, 'standard fan definition1', 'JVEC-SP'],
                                 [134, 'standard fan definition1', 'JVEC-SP'],
                                 [135, 'standard fan definition1', 'JVEC-SP'],
                                 [136, 'standard fan definition1', 'JVEC-SP'],
                                 [137, 'standard fan definition1', 'JVEC-SP'],
                                 [138, 'standard fan definition1', 'JVEC-SP'],
                                 [139, 'standard fan definition1', 'JVEC-SP'],
                                 [140, 'standard fan definition1', 'JVEC-SP'],
                                 [141, 'standard fan definition1', 'JVEC-SP'],
                                 [142, 'standard fan definition1', 'JVEC-SP'],
                                 [143, 'standard fan definition1', 'JVEC-SP'],
                                 [144, 'standard fan definition1', 'JVEC-SP'],
                                 [145, 'standard fan definition1', 'JVEC-SP'],
                                 [146, 'standard fan definition1', 'JVEC-SP'],
                                 [147, 'standard fan definition1', 'JVEC-SP'],
                                 [148, 'standard fan definition1', 'JVEC-SP'],
                                 [149, 'standard fan definition1', 'JVEC-SP'],
                                 [150, 'standard fan definition1', 'JVEC-SP']]
result = {}

for address, fan_definitions_name, fan_type in list_address_of_selected_fans:
    result.setdefault(fan_definitions_name, set()).add(int(address))

print(result)

result ends up being -> {'standard fan definition1': {128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127}}

Why is it doing this? The numbers should be in order such as they are initially in the list_address_of_selected_fans variable.

EDIT2: here is live code showing the issue https://repl.it/talk/share/adding-values-to-defaultdict-set-breaking-on-128/122013

Solution

  • The set() object is an unordered collection (see https://docs.python.org/3.8/library/stdtypes.html#set-types-set-frozenset)

    For your purposes, if you want them in the order in which they originally appeared and you are going to allow repeats, you could swap out your set() and add() for list() and append():

    for address, fan_definitions_name, fan_type in list_address_of_selected_fans:
    result.setdefault(fan_definitions_name, list()).append(int(address))

    If you want to ignore repeats, then you'd have to check for those by creating sets in addition to the lists...:

    result = {}
result_sets = {}

for address, fan_definitions_name, fan_type in list_address_of_selected_fans:
    iaddress = int(address)
    prev_set = result_sets.get(fan_definitions_name, set())
    if (iaddress not in prev_set):
        result.setdefault(fan_definitions_name, list()).append(iaddress)
        result_sets.setdefault(fan_definitions_name, set()).add(iaddress)

    Or, if you want to have it all in one variable and less code, you can accomplish that with OrderedDict like so:

    from collections import OrderedDict
result = {}
for address, fan_definitions_name, fan_type in list_address_of_selected_fans:
    result.setdefault(fan_definitions_name, OrderedDict())[int(address)] = None

print(result['standard fan definition1'].keys())