快速检查是否为空，如果为空，则将其设置为NULL:

Do a quick check for blank, and if it is, set it equal to NULL:

if(!variable_to_insert)
    variable_to_insert = "NULL"

...然后确保插入的变量不在insert语句的引号中，例如:

...then make sure that the inserted variable is not in quotes for the insert statement, like:

insert = "INSERT INTO table (var) VALUES (%s)" % (variable_to_insert)
...

不喜欢:

insert = "INSERT INTO table (var) VALUES ('%s')" % (variable_to_insert)
...