Develop Reference

Passing data between apps in Python

I have a question about implementing passing data between two apps that I have running.
I have a Flask backend, which receives a user email via a POST request and stores it in a variable. I need to pass this variable into TelegramBotAPI.
What I need to happen is when Flask receives a new user email, it will pass the data into the TelegramBotAPI and trigger a function which will send it in a message to the user.
How do I go about implementing this?

Assuming your architecture separates the TelegramBot from the Flask server, you would treat your flask server as the client for your Telegram Bot which is the server in this scenario.
Armed with this information there are numerous ways to go about this. TelegramBot could provide an http server through which clients could send requests. Another option which requires less availability from the Bot but ensures eventual consistency is using a message broker like RabbitMQ.
Lastly, if you wish to store the email permanently you should consider using a storage like a Database (for robustness) or a File system (if you have only one server)

Django: Should sendgrid emails always be sent from Celery?

I'm using django-sendgrid-v5 and I read somewhere that it isn't good to send emails from the main webserver. Should I process emails from Celery? Or is it fine to call from the main app since I'm using an external service like Sendgrid anyways?

I don't know in which context you've read that, but I would guess it has something to do with reliability, spam and security in general.
Short answer: Yes, this should be fully okay as you are using an external email service.
Another option is to set up a Smart host on your webserver and let your main email server deliver it to the final recipients.
Long answer: Nowadays sending emails from a (web)server, which is not fully set up as an email server might be difficult in means of reliably sending emails.
Due to the massive amounts of spam and malware sent, most (or at least a lot) receiving email servers (Mail Exchangers) are trying to check if the emails they should deliver to their users, are legit.
This is done by several settings mostly on the server itself. To name only a few: RDNS, DKIM, Greylisting, etc.
In general a (web) server whos main purpose is not sending emails, does not have all these settings. This might result in difficulties to reach certain email addresses.

Python service/framework to run code

I am having trouble finding an answer to this question.
I am looking for a framework where I can send a python function to a rest endpoint, and it sends a response upon completion.
If there is no precanned solution, what would be a good set of packages to use to do this?

Maybe you could try to use SocketIO with Celery.
SocketIO is an option to create a channel between clients (web, mobile apps, etc) and server.
When received a specific message (you can create you own protocol) you can call a task in a Message Queue using Celery framework with Redis or RabbitMQ.
Maybe you need to use an another framework called Kombu to be able to send a message using the connection in socketio.
You can find some tips on this link: http://python-socketio.readthedocs.io/en/latest/
I hope I could helped.

Async Tasks for Django and Gunicorn

I have a use case where I have to send_email to user in my views. Now the user who submitted the form will not receive an HTTP response until the email has been sent . I do not want to make the user wait on the send_mail. So i want to send the mail asynchronously without caring of the email error. I am using using celery for sending mail async but i have read that it may be a overkill for simpler tasks like this. How can i achieve the above task without using celery

I'm assuming you don't want to wait because you are using an external service (outside of your control) for sending email. If that's the case then setup a local SMTP server as a relay. Many services such as Amazon SES, SendGrid, Mandrill/Mailchimp have directions on how to do it. The application will only have to wait on the delivery to localhost (which should be fast and is within your control). The final delivery will be forwarded on asynchronously to the request/response. STMP servers are already built to handle delivery failures with retries which is what you might gain by moving to Celery.

Best way to do email scheduling on a python web application?

I have a Pyramid web application that needs to send emails such as confirmation emails after registration, newsletters and so forth. I know how to send emails using smtplib in python and I decided on an smtp service (I think sendgrid will do the trick).
The real problem is the scheduling and delay sending of the emails - for example, when a user registers, the email is to be sent on the form post view. But, I don't want to block the request, and therefore would like to "schedule" the email in a non-blocking way.
Other than implementing this myself (probably with a DB and a worker), is there an existing solution to email queue and scheduling?
Thanks!

The existing solution to which you refer is to run your own SMTP server on the machine, bound only to localhost to prevent any other machines from connecting to it. Since you're the only one using it, submitting a message to it should be close to instantaneous, and the server will handle queuing, retries, etc. If you are running on a UNIX/Linux box, there's probably already such a server installed.

In my app, I insert emails in DB table, and I have python script running under cron that checks this table and sends email updating record as sent.

You can also use Redis Lists as a Queue to send emails. Create couple of worker processes which listens a Redis List, and
publish a Email job via RPUSH or LPUSH
receive the job at your worker via LPOP or RPOP
so that your web app worker process won't be affected, or not even feel the overhead for email sending operations.
This design allows you not to care how long does it take to send an email. The email service might be local or a external email service, however you want.