[FIXED] Python/Outlook: Only half of the emails picked up each time

Issue

The background is I have a scheduled job on Unix and this job sent me hundreds of the emails overnight. Every morning I want to save the attachment of these emails. I have written a python snippet for the purpose to automate the process. However, it seems each time when I run the script, only half of the emails(in my target directory) will get processed. So this is what I got from log this morning:

2021-11-18 06:13:30,688 : INFO : utils.util : Before clean up. 335 items in total
2021-11-18 06:13:42,098 : INFO : utils.util : After clean up. 167 items remained
2021-11-18 06:14:17,968 : INFO : utils.util : Before clean up. 167 items in total
2021-11-18 06:14:25,660 : INFO : utils.util : After clean up. 83 items remained
2021-11-18 06:14:34,762 : INFO : utils.util : Before clean up. 83 items in total
2021-11-18 06:14:38,591 : INFO : utils.util : After clean up. 41 items remained
2021-11-18 06:14:47,633 : INFO : utils.util : Before clean up. 41 items in total
2021-11-18 06:14:49,745 : INFO : utils.util : After clean up. 20 items remained
2021-11-18 06:14:56,348 : INFO : utils.util : Before clean up. 20 items in total
2021-11-18 06:14:57,426 : INFO : utils.util : After clean up. 9 items remained
2021-11-18 06:15:15,807 : INFO : utils.util : Before clean up. 9 items in total
2021-11-18 06:15:16,260 : INFO : utils.util : After clean up. 4 items remained
2021-11-18 06:15:22,981 : INFO : utils.util : Before clean up. 4 items in total
2021-11-18 06:15:23,215 : INFO : utils.util : After clean up. 1 items remained
2021-11-18 06:15:36,117 : INFO : utils.util : Before clean up. 1 items in total
2021-11-18 06:15:36,164 : INFO : utils.util : After clean up. 0 items remained

335->167->83->41->20->9->4->1->0

Can you please give me some hints, with regards to what is the potential issue?

Here's my code:

import os
import win32com.client

def get_target_folder(folder: str):
    outlook = win32com.client.Dispatch('outlook.application')
    mapi = outlook.GetNamespace("MAPI")
    target = mapi
    dir = folder.split("\\")
    for d in dir:
        try:
            target = target.Folders(d)
        except:
            logger.error("Current folder path {}. The sub folder {} doesn't exist".format(target.FolderPath, d))
            target = None
            break

    return target


def save_job_status():
    mailfolder= config["OUTLOOK"]["JOBS"]
    keyword = config["OUTLOOK"]["KEYWORD"]
    destination = config["OUTLOOK"]["LOCALDATA"]
    criteria = f"@SQL=\"urn:schemas:httpmail:subject\" like '%{keyword}%'"

    folder = get_target_folder(folder=mailfolder)
    items = folder.items
    emails = items.restrict(criteria)
    logger.info("Before clean up. {} items in total".format(emails.count))

    for email in emails:
        try:
            attachments = email.attachments
            for attachment in attachments:
                filename = attachment.FileName
                attachment.SaveAsFile(os.path.join(destination, filename ))
            email.Delete()
        except:
            logger.error("Can't operate on the email {}".format(email.Subject))
    items = folder.items
    logger.info("After clean up. {} items remained".format(items.count))

As I have also setup outlook rules, all mails go to that "JOBS" folder, in my outlook, are the ones satisfied the condition and should be processed. I setup a "criteria" only for the purpose to avoid operation mistake.

Thank you in advance!

========================Solution Identified======================= After referring to @Dmitry Streblechenko answer, I understood. It's a collection, and I was modifying the collection, while I'm accessing it.

The key modification I did, to resolve this issue is as below

  count = emails.count
        for i in range(count-1, -1, -1):
            print("{} {}".format(i, emails[i].subject))
            emails[i].Delete()

Please note this is a reverse index access, i.e from the largest to the smallest, using a range. As when the bottom of the collection is removed the top ones can still be accessed using the original index.

Solution

Do not use for email in emails: loop if you are modifying the collection (by calling email.Delete()). Use a down loop from emails.Count down to 1.

Answered By - Dmitry Streblechenko