python 3.9 warnings cleared

Author: bgoli

cbmpy/CBModel.py

@@ -5877,7 +5877,7 @@ def createAssociationAndGeneRefsFromTree(self, gprtree, altlabels=None):
                 # print('addGeneRef')
             else:
                 # print('createAssociationAndGeneRefs', gid, label)
-                if gid is None or gid is 'None':
+                if gid is None or gid == 'None':
                     print(self.getTree(), genes, gid, label)
                     continue
                 self.__objref__().addGene(Gene(gid, label, active=True))

cbmpy/CBWrite.py

@@ -3027,7 +3027,7 @@ def convertExcelToFloat(num):
     ## keep this in sync with convertFloatToExcel
     if num == '':
         rval = None
-    elif num is 'nan':
+    elif num == 'nan':
         rval = numpy.nan
     elif num == 'inf':
         rval = numpy.inf

cbmpy/CBXML.py

@@ -277,7 +277,7 @@ def formatSbmlId(s):
             out += x
         else:
             out += '_'
-    if not out[0].isalpha() and out[0] is not '_':
+    if not out[0].isalpha() and out[0] != '_':
         out = '_' + out
     return out