# [Chicago] A list comprehension???

Lewit, Douglas d-lewit at neiu.edu
Tue May 5 02:08:04 CEST 2015

```I've been playing with this, and I think I've got it!!!

Here's what I have:

[sum([2*k for k in range(i)]) for i in range(1, 11)]

I started with sum(2*k for k in range(10)) and noticed that gave me 90, and
then when you substitute range(9) then you get 72, etc.  So.... I think I
got it!  Am I a Python genius or what?!   ;-)

I'm guessing that list comprehensions, set comprehensions, generator
comprehensions, etc, etc are used a lot in functional programming.  I have
this ebook on functional programming in Python.  Some of it is really cool,
and some of it is almost like rocket science to me.... but I'm learning.

> There is a different algorithm, one that doesn't refer to the previous
> item in the list, that produces those numbers. Think about what kind of
> algebraic function generally produces a series of numbers that get farther
> and farther apart.
>
> On Mon, May 4, 2015 at 6:39 PM, Lewit, Douglas <d-lewit at neiu.edu> wrote:
>
>> Hi there,
>>
>> I'm reading this book, "Data Structures & Algorithms in Python" by
>> Goodrich, Tamassia, and Goldwasser.  A pretty good book, it really does
>> into detail about the Python language with various examples.
>>
>> Anyhow, one of the exercises is as follows:
>>
>> Demonstrate how to use Python's list comprehension syntax to produce the
>> list:
>> [0, 2, 6, 12, 20, 30, 42, 56, 72, 90].
>>
>> I'm struggling with this!
>>
>> The best I can do is the following:
>>
>> A = [0]
>> i = 2
>> while i <= 18:
>>     A.append(A[-1] + i)
>>      i+= 2
>>
>> print(A)
>>
>> Well it does work!  BUT it's not a list comprehension!
>>
>> Any suggestions?
>>
>> Thanks,
>>
>> Douglas.
>>
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>>
>>
>
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