在CSV文件中， 以下几种情况字段值需要用半角双引号（即""）将该字段值包含起来（下面简称quoted）：

来源：http://en.wikipedia.org/wiki/Comma-separated_values

1）Fields with embedded commas must be quoted.（当字段值中包含有半角逗号时，整个字段需要quoted），例如：

 1997,Ford,E350,"Super, luxurious truck"

2）Fields with embedded double-quote characters must be quoted, and each of the embedded double-quote characters must be represented by a pair of double-quote characters.（当字段值中含有半角双引号时，整个字段需要quoted，并且被包含的每一个半角双引号都要被替换成一对半角双引号），例如：

 1997,Ford,E350,"Super, ""luxurious"" truck"

3）Fields with embedded line breaks must be quoted (however, many CSV implementations simply do not support this).（当字段值中有换行是，整个字段需要quoted。然而很多CSV模块的实现都不支持字段内有换行。PS：Python是支持的），例如：

1997,Ford,E350,"Go get one now
they are going fast"

4）In CSV implementations that do trim leading or trailing spaces, fields with such spaces as meaningful data must be quoted.（字段值需要以空格开头时，整个字段需要quoted），例如：

 1997,Ford,E350," Super luxurious truck "