Extract attachments from EML files in the current dir, and write them to the output subdir

parseml.py

#!/usr/bin/env python

"""
2020 update:
- More iterators, fewer lists
- Python 3 compatible
- Processes files in parallel
(one thread per CPU, but that's not really how it works)
2021 update:
- Change from legacy format (compat32)
"""

import glob
import os
import email
from email import policy
from multiprocessing import Pool

EXTENSION = "eml"


def extract(filename):
    """
    Try to extract the attachments from all files in cwd

    """
    # ensure that an output dir exists
    od = "output"
    os.path.exists(od) or os.makedirs(od)
    output_count = 0
    try:
        with open(filename, "r") as f:
            msg = email.message_from_file(f, policy=policy.default)
            for attachment in msg.iter_attachments():
                output_filename = attachment.get_filename()
                # If no attachments are found, skip this file
                if output_filename:
                    with open(os.path.join(od, output_filename), "wb") as of:
                        of.write(attachment.get_payload(decode=True))
                        output_count += 1
            if output_count == 0:
                print("No attachment found for file %s!" % f.name)
    # this should catch read and write errors
    except IOError:
        print("Problem with %s or one of its attachments!" % f.name)
    return 1, output_count


if __name__ == "__main__":
    # let's do this in parallel, using cpu count as number of threads
    pool = Pool(None)
    res = pool.map(extract, glob.iglob("*.%s" % EXTENSION))
    # need these if we use _async
    pool.close()
    pool.join()
    # 2-element list holding number of files, number of attachments
    numfiles = [sum(i) for i in zip(*res)]
    print("Done: Processed {} files with {} attachments.".format(*numfiles))