diff --git a/expression.py b/expression.py
index 186c43e..9c4361d 100644
--- a/expression.py
+++ b/expression.py
@@ -1,9 +1,4 @@
-import re
-
-class Token:
-    OPERAND_ADDITION = "+"
-    OPERAND_MULTIPLICATION = "*"
-    NUMBER = re.compile(r'\d+') #CHANGER
+from lexer import Token
 
 class Expression:
 
@@ -23,16 +18,6 @@ class Expression:
             return int(self.val)
 
     def __str__(self):
-        if Token.NUMBER.match(string=self.val) is not None:
-            return self.val
-        return "(" + self.gauche.__str__() + self.val + self.droite.__str__() + ")"
-        
-
-exp = Expression('*',
-Expression(6, None, None),
-Expression('+',
-Expression(4, None, None),
-Expression(3, None, None)
-))
-print(exp.evalue())
-print(str(exp))
\ No newline at end of file
+        if Token.NUMBER.match(str(self.val)) != None:
+            return str(self.val)
+        return "(" + str(self.gauche.__str__()) + str(self.val) + str(self.droite.__str__()) + ")"
diff --git a/lexer.py b/lexer.py
new file mode 100644
index 0000000..34a8e71
--- /dev/null
+++ b/lexer.py
@@ -0,0 +1,6 @@
+import re
+
+class Token:
+    OPERAND_ADDITION = "+"
+    OPERAND_MULTIPLICATION = "*"
+    NUMBER = re.compile(r'\d+') #CHANGER