Flask 和 BytesIO：将文件输出为流的问题答案

【问题标题】：Flask and BytesIO: Problem to output file as a streamFlask 和 BytesIO：将文件输出为流的问题
【发布时间】：2020-06-22 20:07:05
【问题描述】：

我正在尝试将生成的 Excel 文件作为 JSON 有效负载的文件流输出，如下所示：


    def post(self):

        keys = []
        wb = Workbook()
        ws = wb.active

        json_data = request.get_json()


        with NamedTemporaryFile() as tmp:
            for i in range(len(json_data)):
                sub_obj = json_data[i]
                if i == 0:
                    keys = list(sub_obj.keys())
                    for k in range(len(keys)):
                        # row or column index start from 1
                        ws.cell(row=(i + 1), column=(k + 1), value=keys[k]);
                for j in range(len(keys)):
                    ws.cell(row=(i + 2), column=(j + 1), value=sub_obj[keys[j]]);

            wb.save(tmp.name)
            output = BytesIO(tmp.read())
            return output.getvalue()

但这会引发错误

Traceback (most recent call last):
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask/app.py", line 2464, in __call__
    return self.wsgi_app(environ, start_response)
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask/app.py", line 2450, in wsgi_app
    response = self.handle_exception(e)
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask_restful/__init__.py", line 272, in error_router
    return original_handler(e)
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask/app.py", line 1867, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask/_compat.py", line 38, in reraise
    raise value.with_traceback(tb)
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask/app.py", line 2447, in wsgi_app
    response = self.full_dispatch_request()
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask/app.py", line 1952, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask_restful/__init__.py", line 272, in error_router
    return original_handler(e)
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask/app.py", line 1821, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask/_compat.py", line 38, in reraise
    raise value.with_traceback(tb)
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask/app.py", line 1950, in full_dispatch_request
    rv = self.dispatch_request()
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask/app.py", line 1936, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask_restful/__init__.py", line 472, in wrapper
    return self.make_response(data, code, headers=headers)
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask_restful/__init__.py", line 501, in make_response
    resp = self.representations[mediatype](data, *args, **kwargs)
  File "/PythonAPI/flask/env/lib/python3.7/site-packages/flask_restful/representations/json.py", line 21, in output_json
    dumped = dumps(data, **settings) + "\n"
  File "/usr/local/Cellar/python/3.7.4_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/__init__.py", line 238, in dumps
    **kw).encode(obj)
  File "/usr/local/Cellar/python/3.7.4_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/encoder.py", line 201, in encode
    chunks = list(chunks)
  File "/usr/local/Cellar/python/3.7.4_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/encoder.py", line 438, in _iterencode
    o = _default(o)
  File "/usr/local/Cellar/python/3.7.4_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type bytes is not JSON serializable

什么时候

    def post(self):

        keys = []
        wb = Workbook()
        ws = wb.active

        json_data = request.get_json()

        for i in range(len(json_data)):
            sub_obj = json_data[i]
            if i == 0:
                keys = list(sub_obj.keys())
                for k in range(len(keys)):
                    # row or column index start from 1
                    ws.cell(row=(i + 1), column=(k + 1), value=keys[k]);
            for j in range(len(keys)):
                ws.cell(row=(i + 2), column=(j + 1), value=sub_obj[keys[j]]);
        wb.save("test.xlsx")

工作正常。

有没有想过第一个示例中的 JSNO 数据会发生什么变化？

PS。我认为它必须与 Flask API 响应相关，因为默认响应是 JSON，但用

覆盖它

return output.getvalue(), 200, {'content-type': 'application/octet-stream'}

也不行。

【问题讨论】：

发布有关产生异常的代码的问题时，请始终包含完整的 Traceback - 复制并粘贴它，然后将其格式化为代码（选择它并输入 ctrl-k） - 我没有看到任何尝试在您的代码中序列化 (json.dump(s))，除非它发生在请求方法中，在这种情况下您没有提供 minimal reproducible example。
@wwii OP 更新了完整的回溯
@wii OP 更新了该部分代码的已定义函数的完整代码集
您是否尝试依次注释掉最后三行中的每一行，以查看导致问题的原因 - 从 Traceback 中看不出来。那么在找到有问题的线路之后，您是否检查了正在操作的数据？您是否考虑过其中任何一个来修复该数据？ - set object is not JSON serializable, https://stackoverflow.com/questions/8230315/how-to-json-serialize-sets.
@wwii 我只是按照你的建议做了 - 注释掉了行，看起来可能是 Flask 响应 - 输入 JSON 而不是流

标签： python json python-3.x flask flask-restful

【解决方案1】：

通过更改默认的 Flask 响应类型标头来解决它：

    keys = []
    wb = Workbook()
    ws = wb.active

    json_data = request.get_json()

    with NamedTemporaryFile() as tmp:

        for i in range(len(json_data)):
            sub_obj = json_data[i]
            if i == 0:
                keys = list(sub_obj.keys())
                for k in range(len(keys)):
                    # row or column index start from 1
                    ws.cell(row=(i + 1), column=(k + 1), value=keys[k]);
            for j in range(len(keys)):
                ws.cell(row=(i + 2), column=(j + 1), value=sub_obj[keys[j]]);
        wb.save(tmp.name)

        buf = BytesIO(tmp.read())

        response = app.make_response(buf.getvalue())
        response.headers['content-type'] = 'application/octet-stream'

        return response

【讨论】：