diff --git a/command_seq_reader.py b/command_seq_reader.py
index 8e63d35..1c3aff3 100644
--- a/command_seq_reader.py
+++ b/command_seq_reader.py
@@ -21,7 +21,7 @@
 def items_of_interest(dct, types_of_interest):
     return [(k, v) for (k, v) in dct.items() if isinstance(v, types_of_interest)]
 
-def recordingexec(arg, types_of_interest = (int, basestring)):
+def recordingexec(arg, types_of_interest = (int, str)):
     cmdbuf = []
     lastcmd = ''
     commandInProgress = []
@@ -41,14 +41,14 @@ def recordingexec(arg, types_of_interest = (int, basestring)):
             commandInProgress = []
         except IndentationError:
             pass            
-        except SyntaxError, e:
+        except SyntaxError as e:
             if not commandUnfinished.search(str(e)):
                 raise
-        except Exception, e:
-            raise Exception, '%s:\n%s' % (e, line)
+        except Exception as e:
+            raise Exception(f'{e}:\n{line}')
     return (lastcmd, dict(lastlocals))
                    
-def last_assignment_or_evaluatable(s, types_of_interest=(basestring, int, float)):
+def last_assignment_or_evaluatable(s, types_of_interest=(str, int, float)):
     s = s.strip()
     if not s:
         return None
@@ -56,12 +56,12 @@ def last_assignment_or_evaluatable(s, types_of_interest=(basestring, int, float)
     (lastcmd, lastlocals) = recordingexec(s, types_of_interest)
     try:
         return eval(lastcmd)
-    except SyntaxError, e:
+    except SyntaxError as e:
         if 'invalid syntax' not in str(e):
             raise
     if len(lastlocals) > 1:
-        raise ValueError, "Multiple assignments - couldn't determine which one"
-    return eval(lastlocals.keys()[0])
+        raise ValueError("Multiple assignments - couldn't determine which one")
+    return eval(next(lastlocals.keys()))
 
 class RecordingExecTestSuite(unittest.TestCase):
     def testSimpleAssignments(self):
@@ -78,7 +78,7 @@ def testIgnoreObj(self):
 uts = unittest.TestSuite()
 ''', (unittest.TestSuite))
         self.assertEqual(lastcmd, 'uts = unittest.TestSuite()')
-        self.assertEqual(lastlocals.keys(), ['uts'])
+        self.assertEqual(list(lastlocals.keys()), ['uts'])
     def testExecutableLastLine(self):
         (lastcmd, lastlocals) = recordingexec('''
 a = 1
@@ -116,4 +116,4 @@ def testEmpty(self):
     
 if __name__ == '__main__':
     #unittest.main()
-    doctest.testmod()
\ No newline at end of file
+    doctest.testmod()
diff --git a/pyparsing_helper.py b/pyparsing_helper.py
index 5f483a0..a06789b 100755
--- a/pyparsing_helper.py
+++ b/pyparsing_helper.py
@@ -8,7 +8,7 @@
 
 By Catherine Devlin (http://catherinedevlin.blogspot.com)
 '''
-from Tkinter import *
+from tkinter import *
 from command_seq_reader import last_assignment_or_evaluatable
 import pyparsing
 import time, threading, functools, string, optparse, sys
@@ -25,14 +25,14 @@
 def _eq_monkeypatch(self, other):
     if isinstance(other, pyparsing.ParserElement):
         return self.__dict__ == other.__dict__
-    elif isinstance(other, basestring):
+    elif isinstance(other, str):
         try:
             (self + StringEnd()).parseString(_ustr(other))
             return True
-        except ParseBaseException:
+        except pyparsing.ParseBaseException:
             return False
     else:
-        return super(ParserElement,self)==other
+        return super(pyparsing.ParserElement, self) == other
 
 pyparsing.ParserElement.__eq__ = _eq_monkeypatch
 
@@ -79,8 +79,8 @@ def apply_grammar(self, i):
                 result = self.grammar.transformString(target)
             else:                
                 result = self.grammar.parseString(target).dump()
-        except Exception, e:
-            result = '%s\n%s' % (str(e.__class__), str(e))
+        except Exception as e:
+            result = f'{e.__class__}\n{e}'
         self.set_result(i, result)
         
     def set_result(self, i, txt):
@@ -97,14 +97,14 @@ def set_all_results(self, txt):
     def reparse(self, event=None):
         self.grammar = self.grammar_text.get(1.0, END).strip()
         if self.grammar:
-            self.grammar = '%s\n%s' % (self.import_type.get(), self.grammar)
+            self.grammar = f'{self.import_type.get()}\n{self.grammar}'
             try:
                 self.grammar = last_assignment_or_evaluatable(self.grammar, types_of_interest=(pyparsing.ParserElement))
                 for i in range(self.num_targets):
                     self.apply_grammar(i)
-            except Exception, e:
+            except Exception as e:
                 if hasattr(e, 'text'):
-                    errtxt = '%s\n\n%s' % (str(e), e.text)
+                    errtxt = f'{e}\n\n{e.text}'
                 else:
                     errtxt = str(e)
                 self.set_all_results(errtxt)
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..5d2de54
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,3 @@
+[build-system]
+requires = ["setuptools>=46.1.0", "wheel"]
+build-backend = "setuptools.build_meta"