pylint woes

[DFS]

On 5/7/2016 9:36 PM, Chris Angelico wrote:
> On Sun, May 8, 2016 at 11:16 AM, DFS <nospam at dfs.com> wrote:
>> On 5/7/2016 1:01 PM, Chris Angelico wrote:
>>> The suggestion from a human would be to use zip(), or possibly to
>>> change your data structures.
>>
>>
>> Happens like this:
>>
>> address data is scraped from a website:
>>
>> names = tree.xpath()
>> addr  = tree.xpath()
>>
>> I want to store the data atomically, so I parse street, city, state, and zip
>> into their own lists.
>>
>> "1250 Peachtree Rd, Atlanta, GA 30303
>>
>> street = [s.split(',')[0] for s in addr]
>> city   = [c.split(',')[1].strip() for c in addr]
>> state  = [s[-8:][:2] for s in addr]
>> zipcd  = [z[-5:] for z in addr]
>
> So you're iterating over addr lots of times, and building separate
> lists. As an alternative, you could iterate over it *once*, and have a
> single object representing an address.


I like the idea of one iteration, but how?   (I'll be trying myself 
before I check back in)

Remember, it's required to split the data up, to give flexibility in 
sorting, searching, output, etc.

I saw a cool example where someone built a list and used it to do a bulk 
INSERT.  That probably won't work well here, because one of the options 
I give the user is # of addresses to store.  So I do invididual INSERTs 
using the 'for j in range()' method, which makes it easier to track how 
many addresses have been stored.


>> Why is it better to zip() them up and use:
>>
>> for item1, item2, item3 in zip(list1, list2, list3):
>>      do something with the items
>>
>> than
>>
>>
>> for j in range(len(list1)):
>>    do something with list1[j], list2[j], list3[j], etc.
>
> Because 'j' is insignificant here, as is the length of the list.

Sorry, but I don't understand what you mean by insignificant.  j keeps 
track of the position in the list - regardless of the length of the list.


> What
> you're doing is iterating over three parallel lists - not counting
> numbers. Imagine that, instead of lists, you just have *sequences* -
> ordered collections of things. You can follow a recipe without knowing
> the numbers of the individual lines; you just need to know the
> sequence. Here, iterate over this collection:
>
> * Collect ingredients.
> * Cream the butter and the sugar.
> * Sift the salt into the flour.
> * Fold the mixture into an origami crane.
>
> These instructions work whether they're numbered or not.

Again, not following you.


The only reason

for j in range(len(list1)):
     do something with list1[j], list2[j], list3[j], etc.

or

for item1, item2, item3 in zip(list1, list2, list3):
     do something with the items

works is because each list has the same number of items.