Finding the index of a date in a DateTime object python

Question

I have a list that contains dates that I created using:

dates_list = pd.date_range(startdate, num_of_periods, freq = 'MS')

^stored the date range in dates_list

This returns my monthly list of dates correctly if I do print(dates_list).

What I am trying to do is looking for an index number given a specific date in the range. I tried:

dates_list.index(call_date)

^^where call_date is the date I am trying to find the index number of

and I get an error message that reads:

TypeError: 'DatetimeIndex' object is not callable

If I try this same command on a simpler list, ie: simple_list = ['cheese', 'banana', 'mushroom', 'apple' ...] simple_list.index('banana') it returns 1.

How do I get the index value from a list of dates? Is there something I have to do differently?

Any feedback would be appreciated. Thank you.

jpp · Accepted Answer · 2018-05-02 12:53:30Z

You have a DatetimeIndex object, not a list. You can confirm this by printing type(dates_list). DatetimeIndex objects do not have an index method.

You can manually retrieve the index as follows:

dates_list = pd.date_range(start=pd.Timestamp('now').normalize(), periods=10, freq='D')

print(dates_list)

# DatetimeIndex(['2018-05-02', '2018-05-03', '2018-05-04', '2018-05-05',
#                '2018-05-06', '2018-05-07', '2018-05-08', '2018-05-09',
#                '2018-05-10', '2018-05-11'],
#               dtype='datetime64[ns]', freq='D')

res = (dates_list == pd.Timestamp('2018-05-04')).argmax()

# 2

Alternatively, you can use a generator. This method is only advisable for large ranges where you believe the date you require is near the start of your DatetimeIndex.

x = pd.Timestamp('2018-05-04')
res = next((i for i, j in enumerate(dates_list) if j == x), None)

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