How can I process at most a certain number of elements from a list?

Question

Using looping as follows to list n files from a directory:

myfiles = glob.glob("*.xml")
files = len(myfiles)

count = 0
myfiles.sort()
files_to_process = 3
for filename in myfiles:
   count += 1
   print (time.strftime("%I:%M:%S"), count ,'of', files, '|', filename)
   if count == files_to_process:
      break

is there an alternative way to iterate only through n times other than using break?

kg1313 · Answer 1 · 2019-12-11T03:21:35.270

2

myfiles = glob.glob("*.xml")
files = len(myfiles)

myfiles.sort()
files_to_process = 3

for i in range(min(files_to_process, files)):
  print (time.strftime("%I:%M:%S"), i+1 ,'of', files, '|', myfiles[i])

edited Dec 11 '19 at 03:21

answered Dec 11 '19 at 03:05

kg1313

66
5

This is a nice clean solution, but it will give an `IndexError` when there are fewer than three files in the list. – kaya3 Dec 11 '19 at 03:13
Added in a min() to avoid that IndexError - not quite as clean anymore though :) – kg1313 Dec 11 '19 at 03:22

score 1 · Answer 2 · answered Dec 11 '19 at 03:02

1

You can take only the first count file names with myfiles[:count] or itertools.islice(myfiles, count).

answered Dec 11 '19 at 03:02

satoru

31,822
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91
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score 1 · Accepted Answer · answered Dec 11 '19 at 03:02

1

Try this:

myfiles = glob.glob("*.xml")
files = len(myfiles)

count = 0
myfiles.sort()
files_to_process = 3
for filename in myfiles[:files_to_process]:
   count += 1
   print (time.strftime("%I:%M:%S"), count ,'of', files, '|', filename)

answered Dec 11 '19 at 03:02

Paul Whipp

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score 1 · Answer 4 · answered Dec 11 '19 at 03:08

Here's a way using zip: the behaviour is to stop after exhausting whichever sequence is shorter. Zipping with a range also saves you having to manually update a counter.

myfiles = glob.glob("*.xml")
files = len(myfiles)

myfiles.sort()
files_to_process = 3

for filename, count in zip(myfiles, range(1, files_to_process+1)):
    print(time.strftime("%I:%M:%S"), count, 'of', files, '|', filename)

That said, this solution is not idiomatic, and I don't think the code is better than the version using break.

How can I process at most a certain number of elements from a list?

4 Answers4