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I need to iterate through a list of date values in Python and get two dates at a time.

Something along the lines of

import datetime

listdates=[datetime.date(2022, 2, 10),datetime.date(2022, 2, 11),datetime.date(2022, 2, 12),datetime.date(2022, 2, 13),datetime.date(2022, 2, 14)]

for a in listdates:
    print(a,next(a))

The problem is that Python doesn't seem to support iterating through dates like this (see error below)

TypeError                                 Traceback (most recent call last)
~\AppData\Local\Temp/ipykernel_1868/3080882783.py in <module>
      2 
      3 for a in listdates:
----> 4     print(a,next(a))

TypeError: 'datetime.date' object is not an iterator

I'm sure there is something I am missing here, but I need these in date format because I need to pass the date values to a different procedure.

Do I need to do something like convert the values to text and back to dates again? Seems like an awful hack.

Any help would be very much appreciated

Stumbling Through Data Science
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  • `itertools.pairwise` provides this functionality directly (though only on 3.10+). The `itertools` module docs for pre-3.10 provide a recipe for `pairwise` on older Python though. – ShadowRanger Jul 13 '22 at 00:01

2 Answers2

2

Is this what you want to do?

import datetime
listdates=[
    datetime.date(2022, 2, 10),
    datetime.date(2022, 2, 11),
    datetime.date(2022, 2, 12),
    datetime.date(2022, 2, 13),
    datetime.date(2022, 2, 14)
]

for i in range(len(listdates)-1):
    print(listdates[i],listdates[i+1])

Output:

2022-02-10 2022-02-11
2022-02-11 2022-02-12
2022-02-12 2022-02-13
2022-02-13 2022-02-14

Iterators are pointers to the elements of your list. You cant use next on the elements of the list - unless they are iterators themselves.

When you do for x in my_list, x is an element of the list, not an iterator.

That's why you are getting the error, the type date is not an iterator:

'datetime.date' object is not an iterator

This is valid:

l = [1,2,3,4]
my_iterator = iter(l)
print(next(my_iterator))
print(next(my_iterator))
print(next(my_iterator))
print(next(my_iterator))

This is not:

l = ['a','b','c','d']
a = l[0]
print(next(a))
Nilo Araujo
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0

If I understand you correctly, you want to add one day to the date:

one_day = datetime.timedelta(days=1)

for d in listdates:
    print(d, d + one_day)

Prints:

2022-02-10 2022-02-11
2022-02-11 2022-02-12
2022-02-12 2022-02-13
2022-02-13 2022-02-14
2022-02-14 2022-02-15
Andrej Kesely
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