[Chicago] Resolving lists within lists within lists within .....
Mike Tamillow
mikaeltamillow96 at gmail.com
Wed Feb 17 12:50:39 EST 2016
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> 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> 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
>>
>>
>>
>>> On Feb 16, 2016, at 10:44 PM, Lewit, Douglas <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> 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> 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> 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> 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> 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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