问题
The Python script
'''
a
'''
from __future__ import print_function
works well (i.e., does nothing), but
'''
a
'''
'''
b
'''
from __future__ import print_function
causes:
File "C:\test.py", line 8
from __future__ import print_function
SyntaxError: from __future__ imports must occur at the beginning of the file
Why?
https://docs.python.org/2/reference/simple_stmts.html#future says that:
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.
The second example only contains comments and blank lines before the from __future__ import print_function, and yet it doesn't work.
I use Python 2.7.
回答1:
... which seems to be in contradiction with the second example I gave.
No, because those are not comments, they are strings.
The first string is elided from the code as a docstring, but the second string becomes a statement in the code consisting of the string itself. __future__ imports must be before all code-relevant lines, even those that have no effect.
来源：https://stackoverflow.com/questions/38688504/from-future-imports-must-occur-at-the-beginning-of-the-file-what-defines