block nesting error

block nesting error是指代码块嵌套错误。在编写代码时，如果代码块的嵌套层次不正确，就会出现这种错误。例如，在一个if语句中嵌套了另一个if语句，但是没有正确地关闭第一个if语句，就会导致block nesting error。这种错误通常会导致程序无法正常运行，需要仔细检查代码块的嵌套层次，找出错误并进行修正。

相关问题

File "<ipython-input-17-d70cd47a624a>", line 3 return arr ^ IndentationError: expected an indented block

This error message is indicating that there is an indentation problem in the code. In Python, indentation is used to group statements, so it is important to make sure that the code is indented correctly.

In this case, it seems that there is a problem with the indentation of the `return` statement. The `return` statement should be indented to be at the same level as the `if` statement, like this:

def remove_duplicates(arr):
    result = []
    for item in arr:
        if item not in result:
            result.append(item)
    return result

Make sure that all the statements in your code are indented correctly according to their level of nesting.