列表索引超出范围错误python 2.7

Question

I'm creating a bunch of lists that looks like this:

[ObjectId('542de00c763f4a7f558be1cf')]
[ObjectId('545284e7bf2e4ea2778b479d'), ObjectId('542de00c763f4a7f558be1d1')]
...etc

All of them have at least one item. When I run this loop, however:

for agent_id in agent_ids:
    curs_obj = user_coll_obj.find({"agent_id" : str(agent_id)}).distinct("_id")
    temp_list=[]
    for obj in curs_obj:
        temp_list.append(obj)
    # print len(temp_list)
    print "len(temp_list) is" , len(temp_list)
    print "temp_list is" , temp_list
    print "temp_list[0] is", temp_list[0]

I get:

    print "temp_list[0] is", temp_list[0]
IndexError: list index out of range

If I comment out print "temp_list[1] is", temp_list[0] I get:

Len(temp_list) is 2
temp_list is [ObjectId('542de00c763f4a7f558be1cb'), ObjectId('54c123d2bf2e4e140e8b45fc')]
....etc.

Why am I getting the error?

Answer 1

Since it's a loop, I'm assuming that at one point your query returns an empty list for a given agent_id which crashes the script at temp_list[0] since it's empty.

off topic mongo's distinct returns a list so there's no need to loop through it and append it to another list (unless you have a good reason to do so).