Can python list and dictionary be nested infinitely?

Question

Recently I found that python list and dictionary can be nested in multiple level like this

a = {'a1':[{'a2':{'a3':[4,5,6]}}]}

So I'd like to ask is there a technical limit for the nested level? If there isn't, is there a conventional limit for nested level, what's it?

Answer 1

The only limit is memory. Given infinite memory you can nest Python objects infinitely.

Demo:

>>> root = lst = []
>>> levels = 0
>>> while True:
...     lst.append([])
...     lst = lst[-1]
...     levels += 1
...     if levels % 1000000 == 0:  # every 1 million
...         print levels
... 
1000000
2000000
3000000
4000000
5000000
6000000
7000000
8000000
9000000
10000000
11000000
# ....
# [ slower and slower as the system starts to swap ]
# ....
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
MemoryError

For the sake of my sanity I killed it at 30 million objects though.