CODEWITHSUNDEEP
pythonloopsfor-loop
Mars Lee
Mars Lee

Reputation: 1945

How to read 2 value once in for loop by Python?

I have a class,com_and_url, containing 2 variable, com and url. Such as:

a = com_and_url(com, url)

And a file I want to read whose content is like this:

Google
www.google.com
yahoo
www.yahoo.com
facebook
www.facebook.com

So here is the psuedo code:

list_com_and_url = []

for com, url in f:
    list_com_and_url.append( com_and_url( com, url ) )

Can python do this? Thanks for the help!

Upvotes: 1

Views: 88

Answers (4)

Kasravnd
Kasravnd

Reputation: 107287

As an optimized way in term of memory (using iterators and refusing of loading whole of the lines in memory) you can use itertools.tee() to create two independent iterator from your file object (which is an iterator) then use itertools.islice() to put the even lines in f and odd lines in next_f then use zip() function (in python 2 itertools.izip()) to create an iterator contain the pair columns.

from itertools import tee, islice

with open('my_file') as f:
     next_f, f = tee(f)
     next_f, f = islice(f, 0, None, 2), islice(next_f, 1, None, 2)
     list_com_and_url = [com_and_url( com, url ) for com, url in zip(f, next_f)]

Upvotes: 0

njzk2
njzk2

Reputation: 39406

The shortest and (I find) clearest way is using slices:

lines = f.readlines()
for com, url in zip(lines[::2], lines[1::2]):
    # Do stuff

(nota: do not attempt this with files that don't fit in memory)

Upvotes: 1

Hackaholic
Hackaholic

Reputation: 19743

Try this:

list_com_and_url = []
with open('my_file') as f:
    for line in f:
        name, url = line, next(f)
        list_com_and_url.append(zip(name, url))

Upvotes: 2

OneCricketeer
OneCricketeer

Reputation: 191728

You can just read two lines at a time

with open('file.txt') as f:
    lines = f.read().splitlines()
    com_and_url = (lines[i:i+2] for i in range(0, len(lines), 2))

This returns a generator, so to output to a list

print(list(com_and_url))

outputs 

[['Google', 'www.google.com'],
 ['yahoo', 'www.yahoo.com'],
 ['facebook', 'www.facebook.com']]

Upvotes: 0

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