python cursor to list with condition over entry

Question

I have a cursor object in python. I wish to scrape that to a list.

names = []
address = []

for x in curs:
    names.append(x["name"])
    
    if (x["country"]=='USA'):
        address.append(x["country"]+x["pincode"])
    else:
        address.append(x["country"])

this is the way I am iterating. Basically add pincode with country IFF country == USA. Else only country. Above piece works But, I wish to know same can be achieved in better/faster way. Right now it is comparing for in entry in curs the country.

score 2 · Answer 1 · answered Jun 15 '21 at 03:57

2

I can only give a more pythonic style, but sorry to help little on efficiency.

suppose your curs data is somehow like this:

curs = [{"name": "A", "country": "USA", "pincode": "1234"},
        {"name": "B", "country": "UK", "pincode": "5678"}, ]

then we can use:

names = [x["name"] for x in curs]
address = [x["country"] + x["pincode"] if (x["country"] == 'USA') else x["country"] for x in curs]

to get the same output:

['A', 'B']
['USA1234', 'UK']

answered Jun 15 '21 at 03:57

Bowen 404

102
5

Each call on `cursor` with a for loop will fetch every item from the DB. I'm not 100% sure if this works (if you can fetch twice) and even if it did, it takes twice as much time as using the original solution. – ARK1375 Jun 15 '21 at 05:42
thanks, but it's another problem, in which one should add a line <`d = curs.fetchall()`> at top to fetch data only once, and use `d` as the iterable in the following. – Bowen 404 Jun 15 '21 at 07:01

score 0 · Answer 2 · edited Jun 15 '21 at 06:51

From what I read in MySQL cursor docs and this post on Stack Overflow, the code snippet below should work fine.

def decider(val):
    if( val['country'] == 'USA'):
        return val["country"]+ val["pincode"]

    else return
        val["country"]

data = curs.fetchall()
names , adress = map(lambda x: x["names"] , data ) , map(decider , data )

However, since cursor.__iter__() will fetch items one by one from the DB, performance vise I don't think that there is a difference between using a for loop and a map.
If you want to improve your code performance, you have to use async programming. It goes something like this:
Fetch the first row from the DB. Begin fetching the second row. While waiting, perform any action you want on the first row until the second row is fetched.

python cursor to list with condition over entry

2 Answers2