如何在循环结束时触发某些东西？

Question

Is this possible? I want to print lines in my file 5 at a time (to send to an API in a batch). But when I get to the last few lines they never print because there are less than 5, never triggering my if statement to print. SO I figured one way to tackle this is to print the remaining lines when the loop closes.

The current code is messy and redundant but this is the idea:

urls = []
urls_csv = ""
counter = 0

with open(urls_file) as f:
    for line in f:

        # Keep track of the lines we've went through
        counter = counter + 1

        # If we have 5 urls in our list it's time to send them to the API call
        if counter > 5:
            counter = 0
            urls_csv = ",".join(urls) # turn the python list into a string csv list
            do_api(urls_csv) # put them to work

            urls = [] # reset the value so we don't send the same urls next time
            urls_csv = "" # reset the value so we don't send the same urls next time
         # Else append to the url list
         else:
            urls.append(line.strip))

Also - Generally speaking, is there a better way to tackle this?

Answer 1

You can group them into sets of 5 lines at a time with the itertools grouper recipe .

import itertools

def grouper(iterable, n, fillvalue=None):
    args = [iter(iterable)] * n
    return itertools.zip_longest(*args, fillvalue=fillvalue)

with open(...) as f:
    for group in grouper(f, 5, fillvalue=""):
        do_api(",".join([g.strip() for g in group if g]))

Answer 2

What do you think of

urls = []

with open(urls_file) as f:
    while True:
        try:
            for i in range(5):
                urls.append(next(f).rstrip())
            print(urls)  # i.e. you have the list of urls, now use it/put it to work
            urls = []
        except StopIteration:
            print(urls)
            break

with an input file of

line1
line2
line3
line4
line5
line6
line7

it produces

['line1', 'line2', 'line3', 'line4', 'line5']
['line6', 'line7']