Python Csv TypeError: a bytes-like object is required, not ‘str‘

问题描述：

今天在将数据model导出csv的时候，出现了TypeError: a bytes-like object is required, not 'str'，跟之前相比，唯一的区别是当前的python版本是3.8.6的版本，之前是老一点的版本，code完全一样，但是3.8.6的版本出现了异常，原始code如下：

with open(r'D:\MyProjects\test.csv','wb') as csvFile:writer=csv.DictWriter(csvFile,fieldnames=cvaModel().__dict__.keys())writer.writeheader()dic=[item.__dict__ for item in models]writer.writerows(dic)

报错信息如下，在调用writeheader方法的时候，传入的fieldnames数据在内部抛出了异常，显示数据类型有问题：

  File ".\GZipTest.py", line 61, in <module>writer.writeheader()return self.writerow(header)File "D:\SoftDownLoad\MySQL\lib\csv.py", line 154, in writerowreturn self.writer.writerow(self._dict_to_list(rowdict))
TypeError: a bytes-like object is required, not 'str'

问题处理：

对报错的说明：在写入文件的时候，我们提出会遇到rb，wb，w这些指定读取的方式，wb表示的是以二进制形式写入到文件中，而w表达的是以文本形式写入到文件中，所以这里我们只需要将wb更改为w即可：

with open(r'D:\MyProjects\test.csv','w') as csvFile:writer=csv.DictWriter(csvFile,fieldnames=cvaModel().__dict__.keys())writer.writeheader()dic=[item.__dict__ for item in models]writer.writerows(dic)

但是至于为什么之前在老的Python版本下，以同样的code运行并没有出现问题，或许是哪儿的配置不一样，或者跟csv引用的版本有关系，这个倒是没有去细究。

扩展 Pandas读取问题：

除此之外，在用pandas将保存的csv另存为excel的时候，也出现了encoding不对的问题，具体报错信息如下：

Traceback (most recent call last):
File ".\GZipTest.py", line 81, in <module>
c=pd.read_csv(r'D:\MyProjects\test.csv')
File "D:\SoftDownLoad\MySQL\lib\site-packages\pandas\util\_decorators.py", line 311, in wrapper
return func(*args, **kwargs)
File "D:\SoftDownLoad\MySQL\lib\site-packages\pandas\io\parsers\readers.py", line 586, in read_csv
return _read(filepath_or_buffer, kwds)
File "D:\SoftDownLoad\MySQL\lib\site-packages\pandas\io\parsers\readers.py", line 482, in _read
parser = TextFileReader(filepath_or_buffer, **kwds)
File "D:\SoftDownLoad\MySQL\lib\site-packages\pandas\io\parsers\readers.py", line 811, in __init__
self._engine = self._make_engine(self.engine)
return mapping[engine](self.f, **self.options) # type: ignore[call-arg]
File "D:\SoftDownLoad\MySQL\lib\site-packages\pandas\io\parsers\c_parser_wrapper.py", line 69, in __init__
self._reader = parsers.TextReader(self.handles.handle, **kwds)
File "pandas\_libs\parsers.pyx", line 542, in pandas._libs.parsers.TextReader.__cinit__
File "pandas\_libs\parsers.pyx", line 642, in pandas._libs.parsers.TextReader._get_header
File "pandas\_libs\parsers.pyx", line 843, in pandas._libs.parsers.TextReader._tokenize_rows
File "pandas\_libs\parsers.pyx", line 1917, in pandas._libs.parsers.raise_parser_error
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xd4 in position 38: invalid continuation byte

需要在读取csv的时候指定encoding为gbk之后才能正常读取到csv中的数据信息，然后将读取到的数据直接转换为Excel（当然在实际中，除非code需要，基本不会出现这种操作）：

c=pd.read_csv(r'D:\MyProjects\test.csv',encoding='gbk')

c.to_excel(r'D:\MyProjects\test.xlsx',index=False,header=True)

因为一个错误导致的其他连锁反应还挺多的。细节决定成败！感谢支持和建议！

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