Re: [Xen-devel] [PATCH for-next RFC 3/4] pygrub: convert python files with 2to3

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Mar 06, 2019 at 11:46:24AM +0000, Andrew Cooper wrote:
> On 06/03/2019 11:31, Wei Liu wrote:
> > On Tue, Mar 05, 2019 at 05:51:04PM +0000, Andrew Cooper wrote:
> >> On 05/03/2019 16:42, Wei Liu wrote:
> >>> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> >>> ---
> >>> Not sure this works with python 2.4, but it should work with 2.7 since
> >>> the changes look more or less in the same vein as the changes in
> >>> libxl.
> >>>
> >>> The conversion of the import is interesting. This definitely needs
> >>> some testing.
> >>> ---
> >>>  tools/pygrub/src/ExtLinuxConf.py | 16 ++++++++--------
> >>>  tools/pygrub/src/GrubConf.py     | 36 
> >>> ++++++++++++++++++------------------
> >>>  tools/pygrub/src/LiloConf.py     | 16 ++++++++--------
> >>>  3 files changed, 34 insertions(+), 34 deletions(-)
> >>>
> >>> diff --git a/tools/pygrub/src/ExtLinuxConf.py 
> >>> b/tools/pygrub/src/ExtLinuxConf.py
> >>> index d1789bf020..60da960c4b 100644
> >>> --- a/tools/pygrub/src/ExtLinuxConf.py
> >>> +++ b/tools/pygrub/src/ExtLinuxConf.py
> >>> @@ -12,7 +12,7 @@
> >>>  
> >>>  import sys, re, os
> >>>  import logging
> >>> -import GrubConf
> >>> +from . import GrubConf
> >> Relative imports definitely don't exist in Py 2.4
> >>
> >>>  
> >>>  class ExtLinuxImage(object):
> >>>      def __init__(self, lines, path):
> >>> @@ -32,7 +32,7 @@ class ExtLinuxImage(object):
> >>>          self.lines = []
> >>>          self.path = path
> >>>          self.root = ""
> >>> -        map(self.set_from_line, lines)
> >>> +        list(map(self.set_from_line, lines))
> >> This an abuse of map() in the first place, but the automatic
> >> transformation makes the result even more confusing.
> > Right. I tried to find the justification for this transformation but the
> > document doesn't provide that.
> 
> The expected use of map is in the form:
> 
> x = map(fn, y)
> 
> which would leave x as a list in Py2, and a generator in Py3.

Oh, so we should indeed force it to evaluate.

> 
> In most code, wrapping map with list() is the correct transformation to
> make, because a) a lot of code written for Py2 expects it to be a list
> and b) you cant programmatically evaluate whether leaving it in its
> generator form is safe in context.
> 
> For this piece of code (and the other similar examples), map() is not
> the correct construct to use in the first place, and probably wants
> fixing for clarity alone, irrespective of the Py3 transformation.
> 

Sure.

Wei.

> ~Andrew

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