Without using the copy library create a copy of a nested dictionary (Python)

Question

I've got a map of this form:

Weekday -> Object -> Integer

I've tried to do this but am getting some issues down the line to do with a key not existing. The error could exist elsewhere in the code. However, could someone perform a little sanity check for me please?

def deepCopy(self, dictToCopy):
    copy = {"Monday":{}, "Tuesday":{}, "Wednesday":{}, "Thursday":{}, "Friday":{}}
    for day, dicts in dictToCopy.items():
        for object, count in dicts.items():
        copy[day][object] = count
    return copy

Can you please show one or more examples of what the input dictionary looks like? — CrazyChucky, Jan 07 '23 at 00:50
are you just trying to make a deep copy of dictToCopy? If so, the code already exists: from copy import deepcopy copy = deepcopy(dictToCopy) — Galo do Leste, Jan 07 '23 at 00:57
@GalodoLeste While their terminology is admittedly imprecise, I think that's precluded by "without using the copy library". — CrazyChucky, Jan 07 '23 at 01:31

score 0 · Accepted Answer · answered Jan 07 '23 at 02:04

How about:

def deepCopy(dictToCopy):
    days = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]
    return {
        day: {obj: count for obj, count in dictToCopy.get(day, {}).items()}
        for day in days
    }


def test_deepCopy():
    src = {
        "Monday": {
            "thing1": 1,
            "thing2": 3,
        },
        "Wednesday": {
            "thing3": 4,
            "thing5": 1,
        },
    }

    expected = {
        "Monday": {
            "thing1": 1,
            "thing2": 3,
        },
        "Tuesday": {},
        "Wednesday": {
            "thing3": 4,
            "thing5": 1,
        },
        "Thursday": {},
        "Friday": {},
    }

    res = deepCopy(src)
    assert res == expected

    # verify that res is a *copy* -- changing value in src does not
    # change value in res
    src["Monday"]["thing1"] = 2
    assert res == expected

If you have pytest handy you can run the test case by just running example.py, assuming you've saved the above code in example.py.

Without using the copy library create a copy of a nested dictionary (Python)

1 Answers1