32 — Weather: reading JSON from the web

Guide 21 fetched a text file over HTTP; 30 loaded JSON from disk. This guide fetches JSON over HTTP, parses it, and prints a mini weather report.

#Steps

1. Create weather.json — a dict holding another dict (current) and a list of dicts (forecast):

   {
     "city": "Seoul",
     "current": {"temperature": 21, "condition": "sunny", "humidity": 55},
     "forecast": [
       {"day": "Mon", "temperature": 22},
       {"day": "Tue", "temperature": 19},
       {"day": "Wed", "temperature": 24}
     ]
   }
   

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2. Serve the folder with Python's built-in HTTP server, in one terminal:

   python3 -m http.server 8000
   

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   weather.json is now at http://localhost:8000/weather.json.

3. The whole program. Save weather.nme:

   # weather.nme — a mini weather report from a local web server.
   # Run: nme r weather — serve this folder first: python3 -m http.server 8000
   
   import urllib.request
   import json
   
   url = "http://localhost:8000/weather.json"
   with urllib.request.urlopen(url) as response:
       body = response.read().decode("utf-8")
   data = json.loads(body)
   
   city = data["city"]
   current = data["current"]
   forecast = data["forecast"]
   show f"Weather in {city}"
   show f"  now: {current['temperature']} C, {current['condition']}"
   show f"  humidity: {current['humidity']}%"
   show "forecast:"
   for day in forecast:
       show f"  {day['day']}: {day['temperature']} C"
   
   warmest = forecast[0]
   for day in forecast:
       if day["temperature"] > warmest["temperature"]:
           warmest = day
   total = 0
   for day in forecast:
       total = total + day["temperature"]
   average = total / len(forecast)
   show f"warmest day: {warmest['day']} at {warmest['temperature']} C"
   show f"average forecast temperature: {round(average, 1)} C"
   

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   urlopen opens the connection; .decode("utf-8") turns the bytes into a string. json.loads parses it into a dict; the for loops find the warmest day.

4. With the server still running, run it:

   nme r weather
   

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   Weather in Seoul
     now: 21 C, sunny
     humidity: 55%
   forecast:
     Mon: 22 C
     Tue: 19 C
     Wed: 24 C
   warmest day: Wed at 24 C
   average forecast temperature: 21.7 C
   

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5. Korean writes the same report with 말해; the full program is in the Korean guide.

#Try it yourself

Change weather.json to your own city and temperature, then rerun — the server reads the file on every request. Add a "wind" number to current and print it.

#What you learned

• python3 -m http.server 8000 serves JSON files just like text files.
• json.loads(body) turns JSON text into a dict or list.
• A JSON dict can hold dicts and lists, and NME picks them out the same way.
• A report loop and a warmest loop read the whole document step by step.