We Keep Coding

Trigger an email when some a certain file becomes available in some location

newbie here.
I have been learning Python for 3 months now because my team uses it to handle big data. I am almost done fully automating the end-to-end process of producing our monthly financials, except for one crucial step:
I need to trigger an email when the extract becomes available.
Basically, I want to do this:
if file F exists in folder Downstream:
Then send email to self.
I will then confirm running the entire process by replying some code word to this email.
TIA!

You may use Python's email library but usually, the examples are not really straightforward and simple especially if you are new. For this reason, I actually made a package that most likely is enough for your needs regarding sending emails.
Just pip install it:
pip install redmail
Then to solve your problem:
from pathlib import Path
from redmail import EmailSender
email = EmailSender(
host="<YOUR SMTP SERVER>",
port=1,
user_name="you#example.com", # If not needed, don't pass this
password="<YOUR PASSWORD>" # If not needed, don't pass this
)
# Check if file exists
if Path("path/to/file.csv").is_file():
# File does exists, send the email
email.send(
receivers=["you#example.com"],
subject="File is now found",
)
If you want to include a message, pass text and/or html parameters and write the email message as a string. You may also set the receivers as a default (attribute of the email instance) if repeatedly send you an email in different sections of your code.
Red Mail is well tested and well documented open-source library with features such as including attachments, embedding images, templating text or HTML and preformatted errors.
Documentation: https://red-mail.readthedocs.io/en/latest/
Source code: https://github.com/Miksus/red-mail
Note that pathlib is from standard library. It is a handy library for manipulating file paths. You could also use os.path.exists if you prefer that.

Python - Django - cardav - How to implement a server

I have a server application written with Django which has a contacts database.
I wish to add a cardav webservice in order to share my contacts on my phone. I have made many search but I am completely lost.
I found some server as Radical, some API which uses files ... but nothing help me.
I need to implement in my server an API which will return to my Android the list of contact from my databases. What output format should I use ?
Thank you.

Your question seems a bit generic nor do you list what resources you looked at and why you are lost.
This presentation is a little old, but shows the fundamentals on how the *DAV protocols work. Building a CardDAV Client is another great starting point.
CardDAV itself is specified in
RFC 6352, and the related RFCs:
WebDAV,
WebDAV ACL,
etc.
What output format should I use ?
CardDAV requests and responses use
WebDAV,
hence XML.
The actual payload is a
vCard v3.
If you are looking for sample code:
The Apple CalendarServer
is a full-fledged CalDAV/CardDAV server written in Python.
Radicale is another one, but you already found that (be more specific why this isn't helping you, Radicale looks like a great starting point to me).
Finally: I don't think Android has CardDAV support builtin. Presumably you are using a sync plugin?

How can I update a plone page via a script?

I have a large amount of automatically generated html files that I would like to push to my Plone website with a script. I currently generate the files, log into Plone, click edit on each individual page and copy and paste the html into the editor. I'd like to automate this. It would be nice to retain the plone versioning, have a auto generated comment for the edit, and come from a specific user.
I've read and tried Webdav with little luck at getting it working consistently and know that there is a way to connect to plone via ftp, but haven't tried it. I'm not sure if these are the methods that I need.
My google searches aren't leading me to anything useful. Any ideas on where to start looking for a solution to this? Or any tips on implementing it?

You can script anything in Plone via the following methods:
Through-the-web via API calls (e.g. XML-RPC, wsapi, etc.)
The bin/instance run script provided by plone.recipe.zope2instance (See charm for an example of this).
You can also use a migration framework like:
collective.transmogrifier
which allows you to write migration code, and trigger it via GenericSetup or Browser view. Additionally, there are applications written on top of Transmogrifier aimed roughly at what you are describing, the most popular of which is:
funnelweb
I would recommend that you consider using or writing a Transmogrifier "blueprint(s)" to do your import, and execute the pipeline with a tool that makes that easy:
mr.migrator
You can find blueprints by searching PyPI for "transmogrify". One popular set of blueprints is:
quintagroup.transmogrifier
One of the main attractions to the Transmogrifier approach, aside from getting the job done, is the ability to share useful blueprints with others.

I think transmogrifier is the best tool for this job, but this will definitely be a programming task no matter how you do it. It's used for many such migration jobs such as migrating from drupal.

There's an add-on, wsapi4plone.core that pumazi at WebLion started that provides web services for portals which you can then hook into. You can create, modify, delete content via XML-RPC calls. The only caveat is that it doesn't yet work with Collections (criteria specifically).
project: http://pypi.python.org/pypi/wsapi4plone.core
docs: http://packages.python.org/wsapi4plone.core/
You can also do it programmatically by hooking into the ZODB via Python (zopepy or some other method).
These should get you started:
http://plone.org/documentation/kb/manipulating-plone-objects-programmatically/reading-and-writing-field-values - you should be able to get an understanding of accessors and mutators (setters and getters), in your case you are going to be more than likely working with obj.Text (getter) and obj.setText (setter).
https://weblion.psu.edu/trac/weblion/wiki/AutomatingObjectCreation - lots of examples (slightly outdated but still relevant)

http://plone.org/documentation/faq/upload-images-files
Try to enable Webdav or ftp in Plone, then you can access Plone via webdav or ftp clients, pushing the html files. Plone (Zope) will recognises the html files as Pages.

How hard is it to build an Email client? - Python

I'm venturing in unknown territory here...
I am trying to work out how hard it could be to implement an Email client using Python:
Email retrieval
Email sending
Email formatting
Email rendering
Also I'm wondering if all protocols are easy/hard to support e.g. SMTP, IMAP, POP3, ...
Hopefully someone could point me in the right direction :)

The Python language does offer raw support for the needed protocols in its standard library. Properly using then, and, properly parsing and assembling a "modern day" e-mail message, however can be tough to do.
Also, you didn't say if you want to create a graphical interface for your e-mail client -- if you want to have a proper graphical interface -- up to the point of being usable, it is quite a lot of work.
Local e-mail storage would be the easier part - unless you want to properly implement an mbox file format RFC-4155 so that other software can easily read/write the messgaes you have fetched, you can store them in as Python Objects using an ORM or an Object Oriented database, such as ZODB, or MongoDB.
If you want more than a toy e-mail app, you will have a lot of work - properly encoding e-mail headers, for example, server authentication and secure authentication and transport layers, decoding of the e-mail text body itself for non ASCII messages. Although the modules on the Python standard library do implement a lot of that, their documentation falls short on examples - and a complete e-mail client would have to use all of then.
Certainly the place to start an e-mail client, even a toy one, would be taking a look on the most recent RFC's for e-mail (and you will have to pick then from here http://www.ietf.org/rfc/rfc-index since just looking for "email rfc" on google gives a poor result).

I think you will find much of the clients important parts prepackaged:
Email retrieval - I think that is covered by many of the Python libraries.
Email sending - This would not be hard and it is most likely covered as well.
Email formatting - I know this is covered because I just used it to parse single and multipart emails for a client.
Email rendering - I would shoot for an HTML renderer of some sort. There is a Python interface to the renderer from the Mozilla project. I would guess there are other rendering engines that have python interfaces as well. I know wxWidgets has some simple HTML facilities and would be a lot lighter weight. Come to think about it the Mozilla engine may have a bunch of the other functions you would need as well. You would have to research each of the parts.
There is lot more to it than what is listed above. Like anything worth while it won't be built in a day. I would lay out precisely what you want it to do. Then start putting together a prototype. Just build a simple framework that does basic things. Like only have it support the text part of a message with no html. Then build on that.
I am amazed at the wealth of coding modules available with Python. I needed to filter html email messages, parse stylesheets, embed styles, and whole host of other things. I found just about every function I needed in a Python library somewhere. I was especially happy when I found out that some css sheets are gzipped that there was a module for that!
So if you are serious about then dig in. You will learn a LOT. :)

I have made two libraries that solve some of those problems easily:
Sending emails: Red Mail (SMTP)
Receiving emails: Red Box (IMAP)
Here is a short example of both:
from redbox import EmailBox
from redmail import EmailSender
USERNAME = "me#example.com"
PASSWORD = "<PASSWORD>"
box = EmailBox(
host="imap.example.com",
port=993,
username=USERNAME,
password=PASSWORD
)
sender = EmailSender(
host="smtp.example.com",
port=587,
username=USERNAME,
password=PASSWORD
)
Then you can send emails:
email.send(
subject='email subject',
sender="me#example.com",
receivers=['you#example.com'],
text="Hi, this is an email.",
html="""
<h1>Hi,</h1>
<p>this is an email.</p>
""",
attachments={
'data.csv': Path('path/to/file.csv'),
'raw_file.html': '<h1>Just some HTML</h1>',
}
)
Or read emails:
from redbox.query import UNSEEN, FROM
# Select an email folder
inbox = box["INBOX"]
# Search and process messages
for msg in inbox.search(UNSEEN & FROM('they#example.com')):
# Process the message
print(msg.headers)
print(msg.from_)
print(msg.to)
print(msg.subject)
print(msg.text_body)
print(msg.html_body)
# Set the message as read/seen
msg.read()
Red Box fully supports logical operations using the query language if you need complex logical operations. You can also easily access various parts of the messages.
Links, Red Mail:
Source code
Documentation
Links, Red Box:
Source code
Documentation

If I were you, I'd check out the source code of existing email-clients to get an idea: thunderbird, sylpheed-claws, mutt...
Depending on the set of features you want to support, it is a big project.

Depends to what level you want to build the client. You can quickly whip something up with libraries like smtplib for handling conection/data. And tk for a GUI. But again it all depends on the level of finish your after.
A quick basic tool for yourself: Easy. (With libraries)
Writing a full-feutured email client: Hard.
Instead of using a library, you can also find an open source project you can contribute to. I'd recommend having a look at Mailpile

I'm searching for a messaging platform (like XMPP) that allows tight integration with a web application

At the company I work for, we are building a cluster of web applications for collaboration. Things like accounting, billing, CRM etc.
We are using a RESTfull technique:
For database we use CouchDB
Different applications communicate with one another and with the database via http.
Besides, we have a single sign on solution, so that when you login in one application, you are automatically logged to the other.
For all apps we use Python (Pylons).
Now we need to add instant messaging to the stack.
We need to support both web and desktop clients. But just being able to chat is not enough.
We need to be able to achieve all of the following (and more similar things).
When somebody gets assigned to a task, they must receive a message. I guess this is possible with some system daemon.
There must be an option to automatically group people in groups by lots of different properties. For example, there must be groups divided both by geographical location, by company division, by job type (all the programers from different cities and different company divisions must form a group), so that one can send mass messages to a group of choice.
Rooms should be automatically created and destroyed. For example when several people visit the same invoice, a room for them must be automatically created (and they must auto-join). And when all leave the invoice, the room must be destroyed.
Authentication and authorization from our applications.
I can implement this using custom solutions like hookbox http://hookbox.org/docs/intro.html
but then I'll have lots of problems in supporting desktop clients.
I have no former experience with instant messaging. I've been reading about this lately. I've been looking mostly at things like ejabberd. But it has been a hard time and I can't find whether what I want is possible at all.
So I'd be happy if people with experience in this field could help me with some advice, articles, tales of what is possible etc.

Like frx suggested above, the StropheJS folks have an excellent book about web+xmpp coding but since you mentioned you have no experience in this type of coding I would suggest talking to some folks who have :) It will save you time in the long run - not that I'm saying don't try to implement what frx outlines, it could be a fun project :)
I know of one group who has implemented something similar and chatting with them would help solidify what you have in mind: http://andyet.net/ (I'm not affiliated with them at all except for the fact that the XMPP dev community is small and we tend to know each other :)

All goals could be achieved with ejabberd, strophe and little server side scripting
When someone gets assigned to task, server side script could easily authenticate to xmpp server and send message stanza to assigned JID. That its trivial task.
To group different people in groups, it is easily can be done from web chat app if those user properties are stored somewhere. Just join them in particular multi user chat room after authentication.
Ejabberd has option to automatically create and destroy rooms.
Ejabberd has various authorization methods including database and script auth
You could take look at StropheJS library, they have great book (paperback) released. Really recommend to read this book http://professionalxmpp.com/