[Chicago] Resolving lists within lists within lists within .....
Lewit, Douglas
d-lewit at neiu.edu
Thu Feb 18 00:21:54 EST 2016
Hey Massimo,
That one-liner is so cool! Thanks! Simple and gets the job done. Thanks
for sharing.
On Wed, Feb 17, 2016 at 9:48 PM, DiPierro, Massimo <MDiPierro at cs.depaul.edu>
wrote:
> here is a one liner:
>
> def flatten(x):
> return [z for y in x for z in flatten(y)] if isinstance(x,list) else
> [x]
>
>
>
> On Feb 17, 2016, at 9:30 PM, Lewit, Douglas <d-lewit at neiu.edu<mailto:
> d-lewit at neiu.edu>> wrote:
>
> Hi Mark,
>
> Thanks for those links. Yes, Linus Torvalds is quite a legend in his own
> time. I'll be content to become 1% of the programmer that he is! :-)
>
> My original question was simple, "Does Python have a builtin function for
> flattening lists?" It was a very simple question that provoked a very
> strange and hostile thread! I'm not sure why that is. Anyhow, someone
> mentioned itertools.chain( ). Can someone provide a concrete example of
> how that function works? Or is that question inappropriate? And please,
> I'm just asking about itertools.chain( ). I am not asking for any other
> type of reply, okay? Thank you.
>
>
>
> On Wed, Feb 17, 2016 at 2:52 PM, Mark Graves <mgraves87 at gmail.com<mailto:
> mgraves87 at gmail.com>> wrote:
> I don't mean to be argumentative or add to this discussion in a negative
> way.
>
> Could we have a little direction from a higher up around the code of
> conduct here? For reference, this is the only one I found:
>
> http://www.chipy.org/pages/conduct/
>
> I am in support of Doug asking his questions and agree with Adam on this.
> I've met Doug, and sometimes his humor is lost on people through the
> mailing list. If you are bothered, you can always create an email filter.
>
> FWIW, imagine if the developer at the top of this list had been
> discouraged from asking questions about his "unusual" implementation?
>
>
> https://groups.google.com/forum/#!msg/comp.os.minix/dlNtH7RRrGA/SwRavCzVE7gJ
>
> https://groups.google.com/forum/#!topic/comp.os.minix/wlhw16QWltI%5B1-25%5D
>
>
>
>
>
>
>
> On Wed, Feb 17, 2016 at 11:50 AM, Mike Tamillow <
> mikaeltamillow96 at gmail.com<mailto:mikaeltamillow96 at gmail.com>> wrote:
> Yeah, but I generally agree that this list shouldn't be used for help with
> personal programming problems. There is a website called stack overflow as
> well as much documentation that can be consulted for this.
>
> What I like best is when messages come out exposing me to some open source
> tool I have yet to hear about that may be useful.
>
> I'm sure there's other great discussions but I don't think code by email
> is quite a good thing to send out to hundreds of people.
>
> Sent from my iPhone
>
> On Feb 17, 2016, at 10:05 AM, Adam Forsyth <adam at adamforsyth.net<mailto:
> adam at adamforsyth.net>> wrote:
>
> Hey everyone,
>
> Please remember that intentions can be hard to judge on the mailing list.
> I've met Douglas in person and he's a nice guy. Please don't assign motives
> just because there are issues communicating.
>
> Adam Forsyth
> Sponsorship Director, ChiPy
>
>
> On Wed, Feb 17, 2016 at 10:02 AM, Chris Foresman <foresmac at gmail.com
> <mailto:foresmac at gmail.com>> wrote:
> Honestly, Douglas, you come to the list all the time asking for help or
> opinions and then you precede to generally be a jerk to people that respond
> to you. The fact is your solution is sloppy, confusing, and doesn’t work at
> least as far as you originally explained it was supposed to work. Brad
> pointed all this out and suggested a vastly better alternative, and did so
> in an extremely polite way. Your response was just acerbic and doltish.
> Please consider either accepting constructive criticism with humility or
> just stop asking for help.
>
>
> Regards,
> Chris Foresman
> chris at chrisforesman.com<mailto:chris at chrisforesman.com>
>
>
>
> On Feb 16, 2016, at 10:44 PM, Lewit, Douglas <d-lewit at neiu.edu<mailto:
> d-lewit at neiu.edu>> wrote:
>
> Use flattenAgain.... which calls flatten repeatedly until there's no
> change in the list. You have to use BOTH functions!
>
> Sarcasm? What's that?
>
>
> On Tue, Feb 16, 2016 at 10:37 PM, Brad Martsberger <
> bradley.marts at gmail.com<mailto:bradley.marts at gmail.com>> wrote:
> Douglas, I don't know if that was supposed to be sarcastic or what.
>
> In fact, your code does not work.
>
> >>> flatten([[[1, 2], 3], 4])
> [[1, 2], 3, 4]
>
> Looks like it fails to fully flatten the list.
>
> I assumed from your original email you were interested in other
> approaches, so I gave one that looks to me like it's much less complex (no
> need for try/except, no need for indexing, 1 recursive call instead of 3).
> Less complex code is usually easier to reason about and less prone to bugs.
>
> In purely functional languages there is no for loop, so if you want to
> iterate over a list, you have to do it with recursive function calls.
> Recursion stops when there's nothing left in the list, so the base case is
> the empty list. Since iterating over a list is so common in programming, it
> can start to feel like this is the way recursion and lists go together.
>
> But a good rule of thumb is only good if it doesn't trip you up when you
> com across an exception to the rule. In the problem of flattening a list,
> the recursion is down the depth of nesting, not across the list. In this
> case, you can stop flattening when you hit a non-list object, so that's
> your base case.
>
> Brad
>
> On Tue, Feb 16, 2016 at 2:50 PM, Lewit, Douglas <d-lewit at neiu.edu<mailto:
> d-lewit at neiu.edu>> wrote:
> Whether it looks pythonic or not Joshua, it works! Try it before you
> criticize it!!! ;-) In implementing recursive functions on lists, one
> of the base cases is almost always whether the list is empty or not. A
> little lesson I learned from studying lists in Haskell and Ocaml. Hard
> languages for sure, but they made me a stronger programmer when it comes to
> the dreaded "R" ( Recursion ). ;-)
>
>
> On Tue, Feb 16, 2016 at 1:13 PM, Brad Martsberger <bradley.marts at gmail.com
> <mailto:bradley.marts at gmail.com>> wrote:
> > you can get almost there with itertools.chain.from_iterable
>
> It's tempting, but it fails in a lot of ways. It successfully flattens a
> list of lists, but doesn't go any deeper than that and fails completely on
> a list composed of some lists and some non-list objects. You can also get
> the same behavior out of a list comprehension.
>
> Douglas, you have written a recursive function, but I think you've missed
> on what the base case is. The base case is not whether or not you've been
> passed an empty list, but rather whether an element is a list or not (if
> it's not, you don't need any further flattening. Also, all those indices
> don't look very pythonic.
>
> Here is a recursive flatten function that will handle any depth and mixed
> depths at different elements (no indexing required)
>
> def flatten(lst):
> new_list = []
> for element in lst:
> if isinstance(element, list):
> new_list.extend(flatten(element))
> else:
> # This is the base case where the recursion ends
> new_list.append(element)
>
> return new_list
>
> >>> flatten([[1, 1.1], 2, 3, [4, 5, [6, 7, 8]]])
> [1, 1.1, 2, 3, 4, 5, 6, 7, 8]
>
> On Mon, Feb 15, 2016 at 9:09 PM, Joshua Herman <zitterbewegung at gmail.com
> <mailto:zitterbewegung at gmail.com>> wrote:
> The idea of flattening a object or datatype is a functional programming
> technique and not just a part of Ruby and Mathematica According to this
> answer on the programming stack exchange there is no method / function that
> implements flatten for build in Python functions but you can get almost
> there with itertools.chain.from_iterable . See
> http://programmers.stackexchange.com/questions/254279/why-doesnt-python-have-a-flatten-function-for-lists
> .
> On Feb 15, 2016, at 4:12 PM, Lewit, Douglas <d-lewit at neiu.edu<mailto:
> d-lewit at neiu.edu>> wrote:
>
> Hi everyone,
>
> Well it's President's Day and I've got the day off! Hooray!!! Finally
> some time to just relax and mess around. So I'm at my computer playing
> around with Python and wondering how to resolve the issue of multiple lists
> embedded within other lists. I came up with two functions that I think
> solve the problem. But I was wondering if Guido or someone else added a
> builtin function or method that does this automatically for the
> programmer. Or is there an easier way? Okay.... thanks. ( In case you're
> wondering why I called the function "flatten" it's because I know from
> experience that Wolfram Mathematica and Ocaml have these "flatten"
> functions. I think Ruby has something similar, but I haven't played with
> Ruby in a while so I'm not really sure. ) The try: except block is
> important because you can't subscript non-list data structures in Python.
> The IndexError is what you get when you try to index an empty list. So I
> ****think**** my try: except block covers most commonly encountered
> exceptions when working with lists embedded within other lists.
>
> Best,
>
> Douglas.
>
> def flatten(lst):
> if lst == [ ]:
> return lst
> else:
> try:
> return [lst[0][0]] + flatten(lst[0][1:] + lst[1:])
> except TypeError:
> return [lst[0]] + flatten(lst[1:])
> except IndexError:
> return flatten(lst[1:])
>
> def flattenAgain(lst):
> newList = lst[:]
> while newList != flatten(newList):
> newList = flatten(newList)
> return newList
>
>
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