∂wx

Today's weather compared to yesterday.

See @dwxnyc and @dwxdtla for examples.

Requirements

• Python 3.6+, pytz, requests
• For local use
  • Dark Sky API
• For deployment as a Twitter bot on AWS Lambda
  • AWS profile
  • Twitter account, application, and consumer key and access token
  • zappa, tweepy

Local use

• Optional but recommended: create and activate a Python 3.6+ virtualenv, e.g.

  $ python3 -m virtualenv venv
  $ source venv/bin/activate
  

• Install pytz and requests (e.g. pip install -r requirements.txt)
• Add your Dark Sky API key, and the latitude, longitude and timezone of the location to your environment, e.g. for Central Park

  $ export DS_KY="..."
  $ export DWX_LATITUDE="40.782222"
  $ export DWX_LONGITUDE="-73.965278"
  $ export DWX_TZ="US/Eastern"
  

• Then run:

  $ python dwx.py
  Saturday. Mostly cloudy until evening. High of 75 (a little cooler than yesterday).
  

AWS Lambda/zappa deployment of a Twitter bot that posts daily

AWS Lambda is an inexpensive way to post the output of dwx.describe_wx() to Twitter once per day. zappa simplifies Lambda deployment.

• Required for zappa: create and activate a Python 3.6+ virtualenv (see above) and pip install -r requirements.txt
• Install zappa and tweepy to the virtual environment (pip install zappa tweepy)
• Create zappa_settings.json, e.g.

  {
      "dev": {
          "profile_name": "default",
          "s3_bucket": "zappa-abcdefg123",
          "events": [{
             "function": "tweet.check_time_and_post",
             "expression": "cron(0 * * * ? *)"
          }],
          "environment_variables": {
              "DS_KEY": "...",
              "TW_CONSUMERKEY": "...",
              "TW_CONSUMERKEYSECRET": "...",
              "TW_ACCESSTOKEN": "...-...",
              "TW_ACCESSTOKENSECRET": "...",
              "DWX_LATITUDE": "40.782222",
              "DWX_LONGITUDE": "-73.965278",
              "DWX_TZ": "US/Eastern"
          }
      }
  }

  Set profile_name to the name of your AWS profile (see ~/.aws/credentials). Set s3_bucket to something unique (this bucket is used for uploading the application but is otherwise left empty). Configure the environment variables using your API keys and location.
• If you want to tweet at a local time other than 7am, edit post_time in tweet.py and set the first number in the cron schedule to the minute of your chosen time. E.g. if you want to tweet at 03:14am every day, set post_time = datetime.time(3, 14) in tweet.py and "expression": "cron(14 * * * ? *)" in zappa_settings.json (see this issue).
• Deploy and monitor with zappa

  $ zappa deploy dev
  ...
  $ zappa tail dev

A note about time zones and daily jobs

Recurring Lambda functions can be scheduled with cron-like syntax. AWS runs in UT, which means the cron schedules must also be in UT. This is not a problem for jobs that recur all day. But if a job is supposed to run at a particular local time each day (or start/stop at a particular time) it makes things tricky.

The hacky solution is to change to cron configuration every time the clocks go forward or back.

The slightly less hacky solution, which is what ∂wx does when configured as a Twitter bot, is to have Lambda run the function hourly, but check the local time inside the Python application. If it's not the correct local time, the tweet doesn't get posted. This all happens in tweet.py.