Yes, but all objects are not iterables. If you list1.extend(object1) as the cheat sheet describes and object1 has no __iter__, it won't work. Likewise, you can iterate strings, so understanding the target of the iterable will be frustrating for list_of_strings.extend('newstring').
This is better described in python's native help documentation:
$ python
>>> help()
>>> list
searching for extend via '/extend':
| extend(...)
| L.extend(iterable) -- extend list by appending elements from the iterable
