"from future imports must occur at the beginning of the file": 什么定义了文件的开头？

Question

Python脚本

'''
a
'''

from __future__ import print_function

运行良好（即什么都不做），但是

'''
a
'''

'''
b
'''
from __future__ import print_function

原因：

File "C:\test.py", line 8
    from __future__ import print_function
SyntaxError: from __future__ imports must occur at the beginning of the file

为什么？

https://docs.python.org/2/reference/simple_stmts.html#future 表示：

A future statement must appear near the top of the module. The only lines that can appear before a future statement are:

the module docstring (if any),

comments,

blank lines, and

other future statements.

第二个例子在from __future__ import print_function之前只有注释和空行，但它不起作用。

我用的是Python2.7.

Answer 1

... which seems to be in contradiction with the second example I gave.

不，因为那些不是注释，它们是字符串。

第一个字符串作为文档字符串从代码中删除，但第二个字符串成为代码中由字符串本身组成的语句。 __future__ imports must before all code-relevant lines, even those that have no effect.

"from __future__ imports must occur at the beginning of the file": 什么定义了文件的开头？

"from __future__ imports must occur at the beginning of the file": what defines the beginning of the file?

python

comments

"from future imports must occur at the beginning of the file": 什么定义了文件的开头？

"from future imports must occur at the beginning of the file": what defines the beginning of the file?