python 鸡零狗碎

• os.path.join() 可以连接结尾是正反斜线的字符串，不需要特意去掉

   print os.path.join('aa\\','bb\\')# 'aa\bb\'
  

• os.path.join() 是按照路径解释字符串，而非普通字符串

    print os.path.join('aa/','/bb')# '/bb'
  

  这里’/bb’实际上是个根目录的路径，所以把’aa/’挤兑没了

• 即使是r字符串结尾也不能是反斜线（转义符）

    print r'some_path\' # error
  

  print r'some_path\\' # right
  

• python 中模拟 enum
  ```python def __error_enum(**enums): return type(‘__ERROR_CODE’, (), enums)

ERROR_CODE = __error_enum( FILE_ERROR=1100, UNKNOWN_PLATFORM=2100, UNKNOWN_CHANNEL=2200, UNKNOWN_LANGUAGE=2300, )

* python 下载大文件
```python
def download_file(url: str, target_file_name: str, chunk_size: int = 16 * 1024):
    """
        使用python核心库下载大文件
        ref: https://stackoverflow.com/questions/1517616/stream-large-binary-files-with-urllib2-to-file
    """

    response = urlopen(url)
    with open(target_file_name, 'wb') as f:
        while True:
            chunk = response.read(chunk_size)
            if not chunk:
                break
            f.write(chunk)