Updating value in nested Dictionary

Question

I can't figure out how to update a value in a nested dictionary, the value keeps getting overwritten.

I have a list date_list = ['2018AUG15', '2017APR22', '2017MAR05', '2016FEB10', '2016FEB09']

I'm working on building a nested dict and so far I have

import collections

date_list = ['2018AUG15', '2017APR22', '2017MAR05', '2016FEB10', '2016FEB09']
month_ditc = collections.defaultdict(dict)

for x in date_list:

    year = x[:4]
    month = x[4:-2]
    day = x[7:]

    month_ditc[year][month]= day

print month_ditc

which yields

defaultdict(<type 'dict'>, {'2017': {'APR': '22', 'MAR': '05'}, '2016': {'FEB': '09'}, '2018': {'AUG': '15'}})

This is close to what I want. The year and month are updating as I loop through, but the day is not.

I have tried the following but still nothing -

 try:
     month_ditc[year][month] = day
 except KeyError:
     month_ditc[year] = {month:day}

I would like the result to be

defaultdict(<type 'dict'>, {'2017': {'APR': '22', 'MAR': '05'}, '2016': {'FEB': '09','10'}, '2018': {'AUG': '15'}})

@MosesKoledoye I updated the body. If there are multiple days in the same month. I need that reflected in the dict. — franchyze923
– franchyze923, Commented Apr 17, 2017 at 14:05

McGrady · Accepted Answer · 2017-04-17 14:09:56Z

4

Your expected output is not valid dictionary, I suppose you want a list, you can try to use setdefault() method to set default value if key is not already in dict.

setdefault(key[, default])

If key is in the dictionary, return its value. If not, insert key with a value of default and return default. default defaults to None.

import collections

date_list = ['2018AUG15', '2017APR22', '2017MAR05', '2016FEB10', '2016FEB09']
month_ditc = collections.defaultdict(dict)

for x in date_list:

    year = x[:4]
    month = x[4:-2]
    day = x[7:]

    month_ditc[year].setdefault(month, []).append(day)
print dict(month_ditc)

Result:

{'2017': {'APR': ['22'], 'MAR': ['05']}, '2016': {'FEB': ['10', '09']}, '2018': {'AUG': ['15']}}

answered Apr 17, 2017 at 14:09

McGrady

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1 Comment

franchyze923 Over a year ago

Exactly what I needed, thank you for the clear explanation.

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