TypeError: 'NoneType' object is not iterable in Python

问题：

What does error TypeError: 'NoneType' object is not iterable mean?错误TypeError: 'NoneType' object is not iterable是什么意思？

I am getting it on this Python code:我在这个 Python 代码上得到了它：

def write_file(data, filename): # creates file and writes list to it
  with open(filename, 'wb') as outfile:
    writer = csv.writer(outfile)
    for row in data: # ABOVE ERROR IS THROWN HERE
      writer.writerow(row)

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解决方案：

参考一： https://en.stackoom.com/question/GJHh
参考二： https://stackoom.com/question/GJHh