Insert an empty line after __future__ imports (Prop#216979)

[rsaim]

$ cat -n /var/tmp/test.py
     1  from __future__ import absolute_import
     2
     3  os
     4  sys


$ tidy-imports -r /var/tmp/test.py
[PYFLYBY] /var/tmp/test.py: added 'import os'
[PYFLYBY] /var/tmp/test.py: added 'import sys'
[PYFLYBY] /var/tmp/test.py: added mandatory 'from __future__ import division'
[PYFLYBY] /var/tmp/test.py: *** modified ***


$ cat -n /var/tmp/test.py
     1  from __future__ import absolute_import, division
     2  import os
     3  import sys
     4
     5  os
     6  sys

I guess we should insert an empty line in-between line 1 and 2.

-Saim

[asmeurer]

It does the right thing if the __future__ import isn't there yet and it adds it as part of mandatory imports. The reason is when it tries to find an existing block to add the import to in https://github.com/pyflyby/pyflyby/blob/8f83d2f2335419512a8f3d72f21186d4a4a975e0/lib/python/pyflyby/_imports2s.py#L143 it adds a new block if the importing being added is __future__ but it doesn't filter out existing imports that are __future__.

I think it would be easiest to fix this as part of #13. Though we could add a quick fix to filter out __future__ imports in that function completely, if this is a high priority thing to fix (#13 will take longer to fix).

[sac111gp]

Internal ticket: Prop#216979