code refactor

related to #8 (closed):

• I kept changes per commit small, so the number of commits got kind of numerous...

src/icartt/dataset.py

@@ -433,17 +433,17 @@ class Dataset:
         :return: dictionary of all variables
         :rtype: dict of Variable(s)
         """
-        vars = {}  # TODO rename - "vars" is a Python built-in
-        if not self.independentVariable is None: # TODO use "is not None" for readbility
-            vars[self.independentVariable.shortname] = self.independentVariable
-        if not self.independentBoundedVariable is None: # TODO use "is not None" for readbility
-            vars[
+        variables = {}
+        if self.independentVariable is not None:
+            variables[self.independentVariable.shortname] = self.independentVariable
+        if self.independentBoundedVariable is not None:
+            variables[
                 self.independentBoundedVariable.shortname
             ] = self.independentBoundedVariable
 
-        vars = {**vars, **self.dependentVariables, **self.auxiliaryVariables}
+        variables = {**variables, **self.dependentVariables, **self.auxiliaryVariables}
 
-        return vars
+        return variables
 
     def readHeader(self, splitChar=","):
         """Read the ICARTT header (from file)"""