extracting a partially matched string in python

Question

I have a folder in which the files are all named like

"12345input789"

"12345output291"

I want to find each pair of files where the start bit ("12345") matches and perform some operation on both of the files

for file_name in os.listdir(directory):
    if "input" in filename:
         input = os.path.join(directory, file_name)
          # how do i extract the output name string here
    else:
        continue

thanks in advance.

L3viathan · Accepted Answer · 2020-06-24 09:36:25Z

1

You could save all file names in two dictionaries:

inputs, outputs = {}, {}
for file_name in os.listdir(directory):
    if "input" in filename:
         pre, _, post = filename.partition("input")
         inputs[pre] = filename
    elif "output" in filename:
         pre, _, post = filename.partition("output")
         outputs[pre] = filename

# Now you can iterate over all inputs:
for prefix, input_filename in inputs.items():
    output_filename = outputs[prefix]
    do_stuff(input_filename, output_filename)

This will of course crash if there is no matching output file for an input file, so make sure that isn't the case, or handle it.

answered Jun 24, 2020 at 9:36

L3viathan

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3 Comments

Lost1 Over a year ago

partition, very nice! so my solution is to sort os.list.dir and iterated over zip(sorted_file_list, range(len(sorted_file_list))). Then the output file is always index + 1, but that only due to the format of the file name... your solution is nice. I think I am going to need this partition function anyway to fetch the correct name for the output.

L3viathan Over a year ago

Instead of zip(x, range(len(x))) use enumerate(x) (you'll just have to swap the order of the names you're binding).

Lost1 Over a year ago

cool, didn't know about that either. maybe i should ask more questions on stack overflow.

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