On 5/7/2016 9:36 PM, Chris Angelico wrote:
On Sun, May 8, 2016 at 11:16 AM, DFS <nos...@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.
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