class_docstr: A "copy" of a sequence that works by inserting a mask in front
  of the underlying sequence, so that you can mutate it without changing
  the underlying sequence. Effectively behaves as if you could do list(x)
  in O(1) time. The full list API is not supported yet but there's no reason
  in principle it couldn't be.
class_docstr_tok: ["A","``","copy","''","of","a","sequence","that","works","by","inserting","a","mask","in","front","of","the","underlying","sequence",",","so","that","you","can","mutate","it","without","changing","the","underlying","sequence",".","Effectively","behaves","as","if","you","could","do","list","(","x",")","in","O","(","1",")","time",".","The","full","list","API","is","not","supported","yet","but","there","'s","no","reason","in","principle","it","could","n't","be","."]
code: def __setitem__(self, i: int, v: int) -> None:
      i = self.__check_index(i)
      if self.__mask is None:
          self.__mask = {}
      self.__mask[i] = v
  
imports: import array
  import sys
  import warnings
  from random import Random
  from typing import Callable, Dict, Generic, Iterable, Iterator, List, Optional, Sequence, Tuple, TypeVar, Union, overload
  from hypothesis.errors import HypothesisWarning
label_desc: Use image node_id 5 for calling the LazySequenceCopy obj's underlying member method code with example usage: obj.__setitem__(i, v) without return types