Associate iterables and items from a list in a for loop-CodePudding

Is it possible to associate certain iterables in a loop with certain items from a list ? I have two lists to start with (totalpages and arguments) and I need to build up certain URL's.

totalpages = [300, 0]
arguments = ['argument1', 'argument2']
urllst = []

for i in totalpages:
  pages = list(range(0, x 100, 100))
  print(pages)
  for page, argument in zip(pages, arguments):
    urls = 'http://URL' str(page) argument
    urllst.append(urls)

urllst

I would like urllst to be like :

[
'http://URL0argument1',
'http://URL100argument1',
'http://URL200argument1',
'http://URL300argument1',
'http://URL0argument2'
]

CodePudding user response：

Let me write this answer to express my opinion on using index here.

You were very close to the solution, but zip'ped wrong lists finally. Here's what should work:

totalpages = [300, 0]
arguments = ['argument1', 'argument2']
urllst = []

for x, argument in zip(totalpages, arguments):
    for page in range(0, x 100, 100):
        url = f'http://URL{page}{argument}'
        urllst.append(url)

print(urllst)

This iterates over pairs (page_number, argument) made from two initial lists by taking items corresponding to the same indices. I switched to f-string to make string concatenation a bit prettier.

Here's a question about comparing index-based, enumerate-based and zip solutions for such kind of problems.

To ensure that input lists are of equal size, you can use zip(totalpages, arguments, strict=True) - this requires python version 3.10 or newer.

Finally, if you're appending in a loop, you're probably missing an optimisation opportunity: list comprehension would be faster, especially on long inputs.

totalpages = [300, 0]
arguments = ['argument1', 'argument2']
urllst = [
    f'http://URL{page}{argument}'
    for x, argument in zip(totalpages, arguments)
    for page in range(0, x 100, 100)
]

print(urllst)

CodePudding user response：

With short zip (to aggregate elements from each of the iterables) itertools.chain.from_iterable (to treat consecutive inner sequences as a single sequence) approach:

import itertools

urllst = list(itertools.chain.from_iterable(
    [f'http://URL{p}{arg}' for p in range(0, page   100, 100)] 
    for page, arg in zip(totalpages, arguments)))

print(urllst)

The output:

['http://URL0argument1', 'http://URL100argument1', 'http://URL200argument1', 'http://URL300argument1', 'http://URL0argument2']

CodePudding user response：

Printing pages after it has been instantiated as a list of numbers will not give you the proper output. It is simpler to just go through each number in a modified nested for-loop:

totalpages = [300, 0]
arguments = ['argument1', 'argument2']
urllst = []

for i in range(len(totalpages)):
  curr_arg = arguments[i]
  for x in range(0, totalpages[i] 100, 100):
    urls = 'http://URL' str(x) curr_arg
    urllst.append(urls)

print(urls)