How to insert elements from a list into another list containing null values?

Question

I have two lists

l1=[obj1, obj2, obj3,obj4, obj5]

l1 is organized by date except where the date value is 'None'.

I want to insert this list into the first :

l2=[obj9, obj6,obj7,obj8]

I want to respect the date : if obj1.date<obj9.date so obj9 will be placed in l1 after obj1 and the same thing for the others in l2

I tried this code :

 for el in l1:
       for e in l2:
            if e.date<el.date
                 l1.insert(l1.index(el),e)
            else:
                 l1.insert(l1.index(el)+1,e)

Program runs without errors but no result is returned.

Any ideas on how to do this with a pythonic way?

the template where the result will be displayed still load and no list is displayed in — rahma, Oct 04 '17 at 15:34
How do you want objects with a `None` date handled as far as inserting them and maintaining the ordering is concerned? — martineau, Oct 04 '17 at 16:18
This question very much reminds me of [this one](https://stackoverflow.com/q/46564124/1639625), earlier today. Even the wording is very similar... — tobias_k, Oct 04 '17 at 17:33

martineau · Accepted Answer · 2017-10-04T18:45:28.893

You haven't answered my question about how you want to "null" dates handled—by which I assume you mean values of None—so the following may process these correctly.

You did say "but I need obj with null values to be in their indexes" in a comment under a different answer, so I implemented something that does that, otherwise preserving the original order when inserting elements from the second list which can be in any order...and it doesn't seem to run terribly slow (or hang).

import datetime

class Object(object):
    def __init__(self, date_string=None):
        self.date = (date_string if date_string is None else
                     datetime.datetime.strptime(date_string, "%Y%m%d"))

    def __repr__(self):
        return '{}({!r})'.format(self.__class__.__name__,
                                 self.date.strftime("%Y%m%d") if self.date
                                 else None)

obj1 = Object('20171001')
obj2 = Object('20171002')
obj3 = Object(None)
obj4 = Object('20171004')
obj5 = Object('20171005')

obj6 = Object('20171006')
obj7 = Object('20171007')
obj8 = Object('20171008')
obj9 = Object('20171009')

l1 = [obj1, obj2, obj3, obj4, obj5]
l2 = [obj9, obj6, obj7, obj8]

print('Before:')
print(l1)
print(l2)

for elem2 in l2:
    for i, elem1 in enumerate(l1):
        if elem1.date and elem2.date < elem1.date:
            l1.insert(i, elem2)
            break
    else:
        l1.append(elem2)

print('After:')
print(l1)

Output:

Before: [Object('20171001'), Object('20171002'), Object(None), Object('20171004'), Object('20171005')] [Object('20171009'), Object('20171006'), Object('20171007'), Object('20171008')]

After: [Object('20171001'), Object('20171002'), Object(None), Object('20171004'), Object('20171005'), Object('20171006'), Object('20171007'), Object('20171008'), Object('20171009')] `

How to insert elements from a list into another list containing null values?

1 Answers1