On 22/05/2014 00:37, numpy-discussion-requ...@scipy.org wrote: > Message: 4 Date: Wed, 21 May 2014 18:32:30 -0400 From: Warren > Weckesser <warren.weckes...@gmail.com> Subject: Re: [Numpy-discussion] > Easter Egg or what I am missing here? To: Discussion of Numerical > Python <numpy-discussion@scipy.org> Message-ID: > <cagzf1udkdap+yd2sqy9cca6rm4zzfyjjzfv0tieesv_driv...@mail.gmail.com> > Content-Type: text/plain; charset=UTF-8 On 5/21/14, Siegfried Gonzi > <siegfried.go...@ed.ac.uk> wrote: >> >Please would anyone tell me the following is an undocumented bug >> >otherwise I will lose faith in everything: >> > >> >== >> >import numpy as np >> > >> > >> >years = [2004,2005,2006,2007] >> > >> >dates = [20040501,20050601,20060801,20071001] >> > >> >for x in years: >> > >> > print 'year ',x >> > >> > xy = np.array([x*1.0e-4 for x in dates]).astype(np.int) >> > >> > print 'year ',x >> >== >> > >> >Or is this a recipe to blow up a power plant? >> > > This is a "wart" of Python 2.x. The dummy variable used in a list > comprehension remains defined with its final value in the enclosing > scope. For example, this is Python 2.7: > >>>> >>>x = 100 >>>> >>>w = [x*x for x in range(4)] >>>> >>>x > 3 > > > This behavior has been changed in Python 3. Here's the same sequence > in Python 3.4: > >>>> >>>x = 100 >>>> >>>w = [x*x for x in range(4)] >>>> >>>x > 100 > > > Guido van Rossum gives a summary of this issue near the end of this > blog:http://python-history.blogspot.com/2010/06/from-list-comprehensions-to-generator.html > > Warren > > >
[I still do not know how to properly use the reply function here. I apologise.] Hi all and thanks to all the respondes. I think I would have expected my code to be behaving like you said version 3.4 will do. I would never have thought 'x' is being changed during execution. I took me nearly 2 hours in my code to figure out what was going on (it was a lenghty piece of code an not so easy to spot). Siegfried -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
