[Baypiggies] This old dog needs a new trick (aka Feedback on type annotations)

[Glen Jarvis]

This old dog is learning new tricks. Specially Type annotation in the latest version of Python 3.

I have written these instructions and tried to clarify with type annotations. Am I at the latest PEP standard? I need to go back to Guido's and DropBoxes' excellent BayPIGgies talk on the subject.

Here is something I'm trying to specify (yes, I know the actual solution is only a few simple lines) using type annotations.

The sample file in this directory (dmarc.lambda/task3_parse_filenames) is the

type of file that is attached to DMARC emails.

The filename of the file (`google.com!glenjarvis.com!1501372800!1501459199.zip`)

contains four valuable pieces of information:

1. The first field in this filename is the name of the email service provider

   (in this example `google.com`) that received at least one email and applied the

   DMARC policies against it.

2. The second field in this filename is the name of the domain for which the

   DMARC policy was applied (in this example `glenjarvis.com`).

3. The third field in this filename is a Date/Time value represented as an

   integer (number of seconds since Epoch). In this example, this would be

   equivalent to the naive datetime "Sunday, July 30, 2017 00:00:00 AM". This

   represents the beginning date/time of the interval for which the report is

   valid.

4. The fourth and final field in this filename is another Date/Time value

   represented as described above.  In this example, this would be equivalent

   to the naive datetime "Sunday, July 30, 2017 04:59:59 PM". This represents

   the beginning date/time of the interval for which the report is valid.

This task should be a simple function. This skeleton should help describe what

is intended/needed

```

def details_from_filename(dmarc_filename:str):

    ....

    email_provider = "google.com"  # type: str

    domain = "glenjarvis.com"  # type: str

    begin_time = datetime.datetime(2017, 7, 30, 0, 0, 0)  # type: datetime.datetime

    end_time = datetime.datetime(2017, 7, 30, 16, 59, 59)  # type: datetime.datetime

    return [email_provider, domain, begin_time, end_time]

```

Thanks in advance for the awesome feedback! :)

Cheers,

Glen Jarvis
--
I use these email security features:
- PGP keys / Keybase:  https://keybase.io/glenjarvis
- One name: https://onename.com/glenjarvis
- ProtonMail (https://protonmail.com/) for end-to-end encryption
- SPF, DKIM, and DMARC DNS (glenjarvis.com)
- DMARC policy of 'reject' (to reject all mails that don't pass security)

Sent with [ProtonMail](https://protonmail.com) Secure Email.
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