[Tutor] Writing for loop output to csv

[Cameron Simpson]

On 06Sep2018 12:32, Brandon Creech <bdcreech91 at gmail.com> wrote:
>Hi, I am working to forecast the temperatures for the next 5 days using an
>API and a for loop. I would like write the output of this loop to a csv in
>this format::
>
>Columns: City, min1, max1, min2, max2,min3,max3,min4,max4,min5,max5
>data:         Athens,Greece 25.4,26.7....etc.
>                 Nantou,Taiwan 16.18, ......etc
>
>the data prints out on top of each other like this:
>
>Nantou, Taiwan 29.49 20.79
>Nantou, Taiwan 30. 49 21.56

Normally there would be more commas in CSV output, eg:

  Nantou, Taiwan,29.49,20.79

and because "Nantou, Taiwan" is a single string, it would typically look like 
this:

  "Nantou, Taiwan",29.49,20.79

to make that clear, otherwise the embedded comma would make it two CSV columns.

>Code I have:
>
>from forecastiopy import *
>import csv

I see you're importing the csv module, but not using it. [...]

[...snip...]
>for city, coords in cities.items():
>    weather = ForecastIO.ForecastIO( api_key, latitude=coords[0],
>longitude=coords[1] )
>    daily = FIODaily.FIODaily(weather)
>    for day in range(2,7):
>        print(str(city) + " " + str(daily.get_day(day)['temperatureMax']) +
>" " + str(daily.get_day(day)['temperatureMin']))

First a small suggestion. Change this:

  print(str(city) + " " + str(daily.get_day(day)['temperatureMax']) + " " + str(daily.get_day(day)['temperatureMin']))

like this:

  day_data = daily.get_day(day)
  print(str(city) + " " + str(day_data['temperatureMax']) + " " + str(day_data['temperatureMin']))

It fetches the daily data just once and makes your subsequent code easily to 
read and debug.

Second, your actual problem. Your loop is basicly sound, but you're using a 
print call for the output.  The csv module provides a writer object which does 
all the heavy lifting for you: turns strings into quotes strings, puts in 
commas, etc. Try this change:

  csvw = csv.writer(sys.stdout)
  for city, coords in cities.items():
      weather = ForecastIO.ForecastIO( api_key, latitude=coords[0], longitude=coords[1] )
      daily = FIODaily.FIODaily(weather)
      for day in range(2,7):
          day_data = daily.get_day(day)
          csvw.writerow([city, day_data['temperatureMax'], day_data['temperatureMin']])

You'll also need to "import sys" up the top to use the name "sys.stdout".

See how now you're just passing a list of the values to the csv writer?

Cheers,
Cameron Simpson <cs at cskk.id.au>