It is a recursive reference. Your list contains itself, or at least there is some kind of cycle.
Example:
x = []
x.insert(0, x)
# now the repr(x) is '[[...]]'.
The built-in repr for lists detects this situation and does not attempt to recurse on the sub-list (as it normally would), because that would lead to infinite recursion.
Note that ... doesn't necessarily tell you which list is referred to:
y, z = [], []
x = [y, z]
y.insert(0, z)
z.insert(0, y)
# looks the same as it would if y contained y and z contained z.
so repr is not really a complete serialization format for lists.
As to why you're getting them: we're not psychic, and can't fix the problem with your code unless we see the code.
