在单元测试中在哪里导入库？ Python

Question

我必须写一个这样的测试文件：

import unittest

from mylibrary import some_crazy_func

class TestSomething(unittest.TestCase):
    def test_some_crazy_func_that_needs_io_open(self):
        # Opens file
        # Calls function
        # assert outputs

但我不确定应该导入库的“pythonic 位置”在哪里（比如说io）。

是否应该在顶部：

import io
import unittest

from mylibrary import some_crazy_func

class TestSomething(unittest.TestCase):
    def test_some_crazy_func_that_needs_io_open(self):
         expected = ['abc', 'def', 'xyz']
         with io.open('somestaticfile.txt', 'r') as fin:
             outputs = [some_crazy_func(line) for line in fin]
         assert outputs == expected

或者在TestCase的函数内：

import unittest

from mylibrary import some_crazy_func

class TestSomething(unittest.TestCase):
    def test_some_crazy_func_that_needs_io_open(self):
         import io
         expected = ['abc', 'def', 'xyz']
         with io.open('somestaticfile.txt', 'r') as fin:
             outputs = [some_crazy_func(line) for line in fin]
         assert outputs == expected

还是在TestCase函数之前和对象初始化时：

import unittest

from mylibrary import some_crazy_func

class TestSomething(unittest.TestCase):
    import io
    def test_some_crazy_func_that_needs_io_open(self):
         expected = ['abc', 'def', 'xyz']
         with io.open('somestaticfile.txt', 'r') as fin:
             outputs = [some_crazy_func(line) for line in fin]
         assert outputs == expected

Answer 1

见 PEP8：https://www.python.org/dev/peps/pep-0008/#id23

它说，

导入总是放在文件的顶部，就在任何模块 cmets 和 docstrings 之后，在模块全局变量和常量之前。