On Sun, Aug 11, 2013 at 5:29 AM, Gary Herron <gary.her...@islandtraining.com> wrote: > A beginner, on his first program or two, can understand 1, and perhaps > parrot 2 without understanding (or needing to). But the step from there to > 3 is huge. It's folly to dump that on a first-time programmer. (It's > probably even folly to dump that on a seasoned programmer just starting in > Python. I still remember not understanding the explanation for "is" when I > first read it. And it continued to make no sense until I had enough > experience to understand the difference betwen C/C++ assignment to variables > and Python's binding of variables.)
See, that's where the problem is. You will never grok the difference between == and is if you're still thinking about C variables. (Though you *might* be able to explain it by talking solely about char* and the way two C strings can be the same but stored at different places in memory. But that would be unhelpful most of the time.) This is important *early* reading for a new Python programmer: http://mail.python.org/pipermail/tutor/2010-December/080505.html Note that it was originally posted on python-tutor, so it was definitely aimed at the inexperienced. > On 08/10/2013 08:43 PM, Chris Angelico wrote: > Granted, English is a poor litmus test for code. But in this > particular example, we're talking about immutable types (simple > integers), where value and identity are practically the same. A Python > implementation would be perfectly justified in interning *every* > integer, in which case the 'is' would work perfectly here. The > distinction between the two is important when the objects are mutable > (so they have an identity that's distinct from their current values). > > > Granted. But please note: There is *nothing* in that sentence which is fit > for a beginner programmer. ... "immutable", "value/identity", "interning" > ... In one ear and out the other. :-) Right. This isn't my explanation of 'is' and '=='; it's my explanation of why it's important to HAVE an explanation of the aforementioned. :) Though the difference between value and identity is significant and important, and mutability is bound to crop up fairly early on; so really, it's only the concept of interning that would be really advanced. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
