add tryGetKey show usage of defaults / boolean if with walrus

pythonApi/grib_to_arrow.cpp

@@ -224,6 +224,10 @@ PYBIND11_MODULE(gribtoarrow, m)
  ,pybind11::call_guard<pybind11::gil_scoped_release>(), R"EOL(
  Get the key passed to it or if the key is missing returns the user supplied default value 
  )EOL") 
+ .def("tryGetKey", &GribMessage::tryGetKey
+ ,pybind11::call_guard<pybind11::gil_scoped_release>(), R"EOL(
+ Get the key passed to it or if the key is missing returns None 
+ )EOL") 
  .doc() = R"EOL(
  This class provides the ability to access attributes such as the parameterId 
 

src/gribmessage.cpp

@@ -306,6 +306,7 @@ using namespace std;
  double GribMessage::getDoubleParameterOrDefault(string parameterName, double defaultValue) {
  double parameterId;
  auto ret = codes_get_double(h, parameterName.c_str(), &parameterId);
+ std::cout << "ret is " << ret << std::endl;
  return ret == 0 ? parameterId : defaultValue;
  }
 
@@ -324,31 +325,55 @@ using namespace std;
 
  }
 
- template <typename T> 
- T GribMessage::tryGetKey(string parameterName) {
+ std::variant<long, std::string, double, nullptr_t> GribMessage::tryGetKey(string parameterName) {
 
  auto dblDefault = std::nan("");
  long maxLong {std::numeric_limits<long>::max()};
  auto stringDefault = "InTheBlueRidgeMountainsOfViriginaOnTheTrailOfTheLonesomePine";
 
- auto doubleResult = getDoubleParameterOrDefault(parameterName, dblDefault);
- if (doubleResult != dblDefault) {
- //we got the result
- return doubleResult;
- }
- //it wasn't a double or the key doesn't exist
+ std::cout << "Getting key " << parameterName << std::endl;
+
+
  auto longResult = getNumericParameterOrDefault(parameterName, maxLong);
  if (longResult != maxLong) {
- //we got the result
- return longResult;
+ //we got a result but it's possibly a string
+ if (longResult == 0) {
+ auto stringResult = getStringParameterOrDefault(parameterName, stringDefault);
+ std::cout << "Value of string is " << stringResult << std::endl;
+ if(stringResult == stringDefault) {
+ std::cout << "returning long" << longResult << std::endl;
+ return {longResult};
+ } 
+ return {stringResult};
+ }
+ return {longResult};
  }
 
+ //it wasn't a double or the key doesn't exist
+ auto doubleResult = getDoubleParameterOrDefault(parameterName, dblDefault);
+ if (!std::isnan(doubleResult)) {
+ std::cout << "Value of double is " << doubleResult << std::endl;
+ //its not a double but it might be a string key
+ auto stringResult = getStringParameterOrDefault(parameterName, stringDefault);
+ std::cout << "Value of string is " << stringResult << std::endl;
+ if(stringResult == stringDefault) {
+ std::cout << "returning double" << doubleResult << std::endl;
+ return {doubleResult};
+ } 
+ std::cout << "returning string" << stringResult << std::endl;
+ return {stringResult};
+ }
+
+
  auto stringResult = getStringParameterOrDefault(parameterName, stringDefault);
  if (stringResult != stringDefault) {
- return stringResult;
+ std::cout << "its a string " << std::endl;
+ return {stringResult};
  }
 
- return nullptr;
+
+ std::cout << "No result found for key " << parameterName << std::endl;
+ return {nullptr};
 
  }
 

src/gribmessage.hpp

@@ -70,8 +70,9 @@ class GribMessage
  template <typename T> 
  T tryGetParameter(string parameterName, T defaultValue = nullptr);
 
- template <typename T> 
- T tryGetKey(string parameterName);
+ //template <typename T> 
+ //T tryGetKey(string parameterName);
+ std::variant<long, std::string, double, nullptr_t> tryGetKey(string parameterName);
 
  std::shared_ptr<arrow::Table> getData();
  std::shared_ptr<arrow::Table> getDataWithLocations();

tests/test_attributes.py

@@ -1,5 +1,6 @@
 import datetime
 import math
+import polars as pl
 
 class TestFilterMessageId:
  def test_attributes(self, resource):
@@ -58,3 +59,42 @@ def test_default_missingKeys(self, resource):
  #String key does exist should return user specified key
  assert "shorty" == message.getStringParameterOrDefault("elChapo", "shorty")
 
+ def test_tryGetKey(self, resource):
+ from gribtoarrow import GribReader
+
+ # Locations are Canary Wharf,Manchester & kristiansand
+ locations = pl.DataFrame(
+ {"lat": [51.5054, 53.4808, 58.1599], "lon": [-0.027176, 2.2426, 8.0182]}
+ ).to_arrow()
+
+ reader = GribReader(str(resource) + "/gep01.t00z.pgrb2a.0p50.f003").withLocations(locations)
+
+ message = next(iter(reader))
+ #key exists so should get value
+ assert 156 == message.tryGetKey("paramId")
+ #key doesn't exist (deliberate typo and no default specified)
+ assert None == message.tryGetKey("paramid")
+ #key exists should return value
+ assert 90.0 == message.tryGetKey("latitudeOfFirstGridPointInDegrees")
+ #key doesn't exist should return value (NaN)
+ assert None == message.tryGetKey("latitudeOfFirstGridPointInDegreesPleaseBoss")
+ assert "gh" == message.tryGetKey("shortName")
+ #String key does exist should return None
+ assert None == message.tryGetKey("elChapo")
+
+ #The next example it to show how we can use tryGetKey (in c# you can return a bool and use ref)
+ #from python 3.8 we can do this with walrus
+ messages = []
+ for message in reader:
+ msg = pl.from_arrow(message.getDataWithLocations()).with_columns([
+ #We know this columns doesn't exist but want a different default
+ pl.lit(key).alias("Shorty") if(key := message.tryGetKey("elChapo")) else pl.lit("sinaloa").alias("Shorty")
+ ])
+ messages.append(msg)
+
+ df : pl.DataFrame = pl.concat(messages)
+ assert all(x == "sinaloa" for x in df["Shorty"].to_list())
+
+
+
+