utf-8和utf-8-sig

As UTF-8 is an 8-bit encoding no BOM is required and anyU+FEFF character in the decoded Unicode string (even if it’s the firstcharacter) is treated as a ZERO WIDTH NO-BREAK SPACE.

UTF-8以字节为编码单元，它的字节顺序在所有系统中都是一様的，没有字节序的问题，也因此它实际上并不需要BOM(“ByteOrder Mark”)。但是UTF-8 with BOM即utf-8-sig需要提供BOM。

简单的说，utf-8-sig是对字节编码有序的。

这种情况发生在pandas在read csv的时候，如果报错，key error,  File "pandas/index.pyx", line 137, in pandas.index.IndexEngine.get_loc (pandas/index.c:4154)
  File "pandas/index.pyx", line 159, in pandas.index.IndexEngine.get_loc (pandas/index.c:4018)
  File "pandas/hashtable.pyx", line 675, in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:12368)
  File "pandas/hashtable.pyx", line 683, in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:12322)

这种情况要考虑使用utf-8-sig这种编码