How to implement a Flatten Nested List Iterator in Python?

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给定一个嵌套的整数列表，实现一个迭代器以展开它。列表的每个元素可以是整数，也可以是列表（其元素也可能是整数或其他列表）。示例 1：给定列表 [[1, 1], 2, [1, 1]]，通过反复调用 next()，得到输出：1, 1, 1, 1, 2。

Given a nested list of integers, implement an iterator to flatten it.

Each element is either an integer, or a list – whose elements may also be integers or other lists.

Example 1:
Given the list [[1,1],2,[1,1]],

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1].

Example 2:
Given the list [1,[4,[6]]],

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,4,6].

/**
* // This is the interface that allows for creating nested lists.
* // You should not implement it, or speculate about its implementation
* public interface NestedInteger {
*
* // @return true if this NestedInteger holds a single integer, rather than a nested list.
* public boolean isInteger();
*
* // @return the single integer that this NestedInteger holds, if it holds a single integer
* // Return null if this NestedInteger holds a nested list
* public Integer getInteger();
*
* // @return
public class NestedIterator implements Iterator<Integer> {

Stack<Iterator<NestedInteger>> stk;
Iterator<NestedInteger> tempIter;
Integer temp = null;
public NestedIterator(List<NestedInteger> nestedList) {
stk = new Stack<Iterator<NestedInteger>>();
tempIter = nestedList.iterator();
temp = findNextInt();
}

@Override
public Integer next() {
int res = temp;
temp = findNextInt();
return res;
}

public Integer findNextInt() {
while (tempIter.hasNext() || !stk.isEmpty()) {
if (tempIter.hasNext()) {
NestedInteger i = tempIter.next();
if (i.isInteger()) {
return i.getInteger();
} else {
stk.push(tempIter);
tempIter = i.getList().iterator();
}
} else {
tempIter = stk.pop();
}
}
return null;
}

@Override
public boolean hasNext() {
return temp != null;
}
}

/**
* Your NestedIterator object will be instantiated and called as such:
* NestedIterator i = new NestedIterator(nestedList);
* while (i.hasNext()) v[f()] = i.next();
*/