Yahoo Weather Forecast

Getting the Yahoo Weather Forecast

As long as Yahoo provides this service, weather conditions and forecasts can be retrieved through their Yahoo Weather API.

Once you know how this works, it’s actually pretty simple, but isn’t that with most things?

SQL Like Weather Query

As you can see on this Yahoo Weather Developer Network page, a SQL like query can be used to retrieve weather information.
If you’re familiar with SQL, then this should look familiar:

SELECT * FROM weather.forecast WHERE woeid IN (SELECT woeid FROM geo.places(1) WHERE text="nome, ak")

Here we get the forecast for Nome, AK (USA), but we let Yahoo figure out what the ID is for that town by doing a subquery:

SELECT woeid FROM geo.places(1) WHERE text="nome, ak"

The returned answer, “woeid”, will then be used in the main query to retrieve the weather forecast, where the location ID (woeid) that came from our subquery, matches the location ID (woeid) of the weather.forecast table.

Weather Forecast: JSON or XML?

We also see that information can be retrieved as JSON data or as XML data. I choose JSON in my unit, since JSON works smooth and has little overhead. XML has caused me enough headaches in the past, so I’m trying to avoid that one.

Making a URL to retrieve Yahoo Weather Forecasts

Let’s look at the URL, for retrieving weather conditions and forecasts, you can find it at the bottom of this Yahoo Weather Developer page:

https://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20weather.forecast%20where%20woeid%20in%20(select%20woeid%20from%20geo.places(1)%20where%20text%3D%22nome%2C

%20ak%22)&format=json&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys

Now keep in mind what we were doing:

• Get the weather for “Nome, AK” (I’ve never been there, but that’s irrelevant I suppose),
• Make sure we get it in JSON format

The base of the URL is:

https://query.yahooapis.com/v1/public/yql?q=...

Followed by the SQL query that we just looked at, however it’s written in HTML save character codes (called URL Encoding, or Percent-encoding, ie. a space becomes %20, which is hex 20, which is decimal 32, which is the ASCII code for a space).

select%20*%20from%20weather.forecast%20where%20woeid%20in%20(select%20woeid%20from%20geo.places(1)%20where%20text%3D%22nome%2C%20ak%22)...

See the text%3D%22nome%2C%20ak%22 part?
Translated in normal characters it says: test=”nome, ak”

So this is where we can pass the text to determine location. The space just before “ak” is actually not even needed, and upper or lowercase doesn’t matter either. If your location however has spaces or special characters in it, then you’d need to URL encode these, so in my unit I added a function to that automatically.

Note though that sometimes you’ll need to provide more information when it comes to passing the location.

For example, when looking for “Osceola, WI”. If I’d provide “osceola,usa”, then you’d get into trouble, since there are multiple towns called Osceola in the USA. The query would only return the first Osceola it found, which happens to be “osecola,fl” – in Florida. So don’t forget to add the state where application: “osceola,wi,usa” (“usa” would not even be needed since it’s in the US).

For cities in different countries, just the city name and country name, is often sufficient.
For example “breda,netherlands”.
With some testing I discovered that you might be able to get away with writing the country name in it’s native notation, so in the previous example: “breda,nederland”. Which works as well.

This part is followed by defining the output format (JSON!).

&format=json...

The rest is just some additional info we need to add, but you don’t need to worry about that:

&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys

So now we know how to build the query.
I’m just explaining it here, so you can read through my code and understand better, which is what.

The Yahoo Weather Forecast Unit

Like I said before, I made a little Pascal unit which handles this just nicely – keep in mind that there is always room for improvement.

Yahoo Weather Forecast in a Record

To get a readable result, I decided to have the main function return a record holding all the data.

The JSON data will automatically be taken apart and stored in this record (TYahooForecast). Since Yahoo includes the forecast for 10 days, I create another record format which can hold the specifics for one day (see the forcast in the TYahooForecast below).

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  TDayForcast = record

    code:string;

    date:string;

    day:string;

    high:string;

    low:string;

    text:string;

  end;



  TYahooForecast = record

    success:boolean;

    distance:string;

    pressure:string;

    speed:string;

    temperature:string;

    location_city:string;

    location_country:string;

    location_region:string;

    wind_chill:string;

    wind_direction:string;

    wind_speed:string;

    atmosphere_humidity:string;

    atmosphere_pressure:string;

    atmosphere_rising:string;

    atmosphere_visibility:string;

    astronomy_sunrise:string;

    astronomy_sunset:string;

    location_latitude:string;

    location_longitude:string;

    last_updated:string;

    current_code:string;

    current_date:string;

    current_temp:string;

    current_text:string;

    forecast: array [0..9] of TDayForcast;

  end;

To get the forecast, we simply call:

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// using defaults (in Celsius)

tmpData := GetYahooForecast('nome, ak'); 



// forcing Fahrenheit

tmpData := GetYahooForecast('nome, ak','f'); 



// forcing Celsius

tmpData := GetYahooForecast('nome, ak','c');

You can add special characters and spaces in the location name, URL Encoding will be handled automatically.

The first thing to check in this example is if everything went OK. You can read that in the “success” field of the record.

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  if tmpData.success then

    begin

      with tmpData do

        begin

          memo1.lines.add('Distance units: '+distance);

          memo1.lines.add('Pressure units: '+pressure);

          ...

        end;

    end

  else

    // FAILED RETRIEVING DATA

As you can see, it’s easy to access the results.

One thing to keep in mind, is the 10 day forecast, which you access like so:

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for Counter:=0 to 9 do

  begin

    memo1.lines.add('Code: '+tmpdata.forecast[Counter].code);

    memo1.lines.add('Date: '+tmpdata.forecast[Counter].date);

    memo1.lines.add('Day: ' +tmpdata.forecast[Counter].day);

    memo1.lines.add('High: '+tmpdata.forecast[Counter].high);

    memo1.lines.add('Low: ' +tmpdata.forecast[Counter].low);

    memo1.lines.add('Text: '+tmpdata.forecast[Counter].text);

  end;

The Unit

This is the code for the unit I created.
Note that it uses Synapse, which can be dowloaded for free. You do not need to install it – in fact, on my Mac it will not even install. Simply unzip the downloaded file and copy all the files from “/source/lib” into your project directory.

You can copy and paste the code, or download it (includes a small example application):

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unit YahooWeather;



{  Unit to retrieve Yahoo Weather Forecast



   (C)2015 Hans Luijten, //www.tweaking4all.com

   Version 1.0



   Uses:  Synapse (http://synapse.ararat.cz/,

          fpjson  (Comes with Lazarus)

          openssl (part of synapse, weather is retrieved with https://)



   Common use:

          GetYahooForecast(location);



          Retrieves current weather and weather forecast, and returns this in a record for easy access.

}



{$mode objfpc}{$H+}



interface



uses

  Classes, SysUtils, httpsend, ssl_openssl, fpjson, jsonparser;



type

  TDayForcast = record

    code:string;

    date:string;

    day:string;

    high:string;

    low:string;

    text:string;

  end;



  TYahooForecast = record

    success:boolean;

    distance:string;

    pressure:string;

    speed:string;

    temperature:string;

    location_city:string;

    location_country:string;

    location_region:string;

    wind_chill:string;

    wind_direction:string;

    wind_speed:string;

    atmosphere_humidity:string;

    atmosphere_pressure:string;

    atmosphere_rising:string;

    atmosphere_visibility:string;

    astronomy_sunrise:string;

    astronomy_sunset:string;

    location_latitude:string;

    location_longitude:string;

    last_updated:string;

    current_code:string;

    current_date:string;

    current_temp:string;

    current_text:string;

    forecast: array [0..9] of TDayForcast;

  end;



function GetYahooWeatherData(Location:string; AsJSON:boolean =true; TemperatureUnits:string = 'c'):string;

function GetYahooForecast(Location:string; TemperatureUnits:string = 'c'):TYahooForecast;

function YahooURLEncode(s: string): string;



implementation



{

  URLEncode



  Encodes string to be suitable as an URL.



  Example: myencodeURL:=YahooURLEncode(myURL);

}

function YahooURLEncode(s: string): string;

var

  i: integer;

  source: PAnsiChar;

begin

  result := '';

  source := pansichar(s);

  for i := 1 to length(source) do

    if not (source[i - 1] in ['A'..'Z', 'a'..'z', '0'..'9', '-', '_', '~', '.', ':', '/']) then

      result := result + '%' + inttohex(ord(source[i - 1]), 2)

    else

      result := result + source[i - 1];

end;



{ Retrieve Yahoo Weather with forcast and place it in a record for easy access



  MyYahooForcast := GetYahooForecast('town,country',true,'c')

}

function GetYahooForecast(Location:string; TemperatureUnits:string = 'c'):TYahooForecast;

var JSONData:TJSONData;

    RawData:string;

    tmpData:TYahooForecast;

    Counter:integer;

begin

  RawData := GetYahooWeatherData(Location,true,TemperatureUnits);



  Counter:=0;

  while ((RawData='') or (pos('ERROR',RawData)>0)) and (Counter<3) do

    begin

      RawData := GetYahooWeatherData(Location,true,TemperatureUnits);

      inc(Counter);

    end;



  if ((RawData='') or (pos('ERROR',RawData)>0)) then

    tmpData.success:=false

  else

    begin

      JSONData := GetJSON(RawData);



      with tmpdata do

        begin

          success:=true;



          distance:=JSONData.FindPath('query.results.channel.units.distance').AsString;

          pressure:=JSONData.FindPath('query.results.channel.units.pressure').AsString;

          speed:=JSONData.FindPath('query.results.channel.units.speed').AsString;

          temperature:=JSONData.FindPath('query.results.channel.units.temperature').AsString;



          location_city:=JSONData.FindPath('query.results.channel.location.city').AsString;

          location_country:=JSONData.FindPath('query.results.channel.location.country').AsString;

          location_region:=JSONData.FindPath('query.results.channel.location.region').AsString;



          wind_chill:=JSONData.FindPath('query.results.channel.wind.chill').AsString;

          wind_direction:=JSONData.FindPath('query.results.channel.wind.direction').AsString;

          wind_speed:=JSONData.FindPath('query.results.channel.wind.speed').AsString;



          atmosphere_humidity:=JSONData.FindPath('query.results.channel.atmosphere.humidity').AsString;

          atmosphere_pressure:=JSONData.FindPath('query.results.channel.atmosphere.pressure').AsString;

          atmosphere_rising:=JSONData.FindPath('query.results.channel.atmosphere.rising').AsString;

          atmosphere_visibility:=JSONData.FindPath('query.results.channel.atmosphere.visibility').AsString;



          astronomy_sunrise:=JSONData.FindPath('query.results.channel.astronomy.sunrise').AsString;

          astronomy_sunset:=JSONData.FindPath('query.results.channel.astronomy.sunset').AsString;



          location_latitude:=JSONData.FindPath('query.results.channel.item.lat').AsString;

          location_longitude:=JSONData.FindPath('query.results.channel.item.long').AsString;



          last_updated:=JSONData.FindPath('query.results.channel.item.pubDate').AsString;



          current_code:=JSONData.FindPath('query.results.channel.item.condition.code').AsString;

          current_date:=JSONData.FindPath('query.results.channel.item.condition.date').AsString;

          current_temp:=JSONData.FindPath('query.results.channel.item.condition.temp').AsString;

          current_text:=JSONData.FindPath('query.results.channel.item.condition.text').AsString;



          for Counter:=0 to 9 do

            begin

              with tmpData.forecast[Counter] do

                begin

                  code:=JSONData.FindPath('query.results.channel.item.forecast['+IntToStr(Counter)+'].code').AsString;

                  date:=JSONData.FindPath('query.results.channel.item.forecast['+IntToStr(Counter)+'].date').AsString;

                  day:=JSONData.FindPath('query.results.channel.item.forecast['+IntToStr(Counter)+'].day').AsString;

                  high:=JSONData.FindPath('query.results.channel.item.forecast['+IntToStr(Counter)+'].high').AsString;

                  low:=JSONData.FindPath('query.results.channel.item.forecast['+IntToStr(Counter)+'].low').AsString;

                  text:=JSONData.FindPath('query.results.channel.item.forecast['+IntToStr(Counter)+'].text').AsString;

                end;

            end;

       end;

    end;



  GetYahooForecast := tmpData;

end;



{ Retrieve Yahoo Weather information



  myString := GetYahooWeatherData('town,country',true,'c');



  Location: typically use town,country, for example: 'osceola,wi.usa', 'amsterdam,netherlands', 'breda,nederland'

  AsJSON  : return as a JSON string if TRUE, otherwise in XML format (JSON default)

  TemperatureUnits: 'c' for Celcius, and 'f' for Fahrentheit         (C default)

}

function GetYahooWeatherData(Location:string; AsJSON:boolean =true; TemperatureUnits:string = 'c'):string;

var HTTPSender : THTTPSend;

    tmpData : TStringList;

    resultString, resultFormat: String;

begin

  if Location='' then

    GetYahooWeatherData:='ERROR: Missing Location'

  else

    begin

      if AsJSON then

        resultFormat := 'json'

      else

        resultFormat := 'xml';



      tmpData    := TStringList.Create;

      HTTPSender := THTTPSend.Create;



      try

        HTTPSender.HTTPMethod('GET',

                              'https://query.yahooapis.com/v1/public/yql?'+

                                'q=select%20*%20from%20weather.forecast%20where%20woeid%20in%20('+                           // get forecast

                                  'select%20woeid%20from%20geo.places(1)%20where%20text%3D%22'+YahooURLEncode(Location)+'%22)'+              // find location based on string

                                '%20and%20u%3D%22'+TemperatureUnits+'%22'+                                                   // force units (c or f)

                                '&format='+resultFormat+'&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys');



        if (HTTPSender.ResultCode >= 100) and (HTTPSender.ResultCode<=299) then

          tmpData.LoadFromStream(HTTPSender.Document)

      finally

        HTTPSender.Free;

      end;



      if tmpData.Text='' then

        resultString:='ERROR: Unable to retrieve data'

      else

        resultString:=tmpData.Text;



      tmpData.Free;



      GetYahooWeatherData := resultString;

    end;

end;



end.

Extra Info: Yahoo Weather Codes

Yahoo Weather also returns a code for each forecast and the current conditions. This code is used to verbalize the conditions.

Here is a list of what these codes mean, which can be practical if you’d like to translate the condition text. Obviously, for English speaking users, this list is not relevant since Yahoo already returns a similar text in the “text” (for each day) and “current_text” (for today) fields.

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const YahooWeatherCondition : array[0..48] of string = ('tornado',

                                                        'tropical storm',

                                                        'hurricane',

                                                        'severe thunderstorms',

                                                        'thunderstorms',

                                                        'mixed rain and snow',

                                                        'mixed rain and sleet',

                                                        'mixed snow and sleet',

                                                        'freezing drizzle',

                                                        'drizzle',

                                                        'freezing rain',

                                                        'showers',

                                                        'showers',

                                                        'snow flurries',

                                                        'light snow showers',

                                                        'blowing snow',

                                                        'snow',

                                                        'hail',

                                                        'sleet',

                                                        'dust',

                                                        'foggy',

                                                        'haze',

                                                        'smoky',

                                                        'blustery',

                                                        'windy',

                                                        'cold',

                                                        'cloudy',

                                                        'mostly cloudy (night)',

                                                        'mostly cloudy (day)',

                                                        'partly cloudy (night)',

                                                        'partly cloudy (day)',

                                                        'clear (night)',

                                                        'sunny',

                                                        'fair (night)',

                                                        'fair (day)',

                                                        'mixed rain and hail',

                                                        'hot',

                                                        'isolated thunderstorms',

                                                        'scattered thunderstorms',

                                                        'scattered thunderstorms',

                                                        'scattered showers',

                                                        'heavy snow',

                                                        'scattered snow showers',

                                                        'heavy snow',

                                                        'partly cloudy',

                                                        'thundershowers',

                                                        'snow showers',

                                                        'isolated thundershowers',

                                                        'not available');

With a simple procedure you can convert the code to text, assuming you defined a variable or constant array like the one above.
Codes > 48 will result in a “not available”.

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function WeatherCode2String(code:string):string;

var intCode:integer;

begin

  try

    intCode:=StrToInt(code)

  except

    intCode:=3200

  end;



  if (intCode<0) or (intCode>47) then

    WeatherCode2String:= YahooWeatherCondition[48]

  else

    WeatherCode2String:= YahooWeatherCondition[intCode]

end;