move __str__ from expression to renderable

pymath/calculus/abstract_polynom.py

@@ -427,7 +427,7 @@ class AbstractPolynom(Explicable):
         return ans
 
     def replace_letter(self, letter):
-        """ Replace the letter in the expression
+        r""" Replace the letter in the expression
 
         :param letter: the new letter.
         :returns: The expression with the new letter.

pymath/calculus/expression.py

@@ -73,14 +73,6 @@ class Expression(Explicable):
         self.steal_history(exp)
         self._isExpression = 1
 
-    def __str__(self):
-        """
-        Overload str
-
-        If you want to changer render use Expression.set_render(...) or use tmp_render context manager.
-        """
-        return self.STR_RENDER(self.postfix_tokens)
-
     def simplify(self):
         """ Compute entirely the expression and return the result with .steps attribute """
         try:
@@ -177,7 +169,7 @@ class Expression(Explicable):
 
     @classmethod
     def develop_steps(cls, tokenList):
-        """ 
+        r""" 
         From a list of tokens, it develops steps of each tokens and transpose it into steps respecting the stucture of the tokenList.
 
         It try to use 'explain' method for every tokens. After using this methode, tokens becom amnesiac.
@@ -186,8 +178,14 @@ class Expression(Explicable):
         >>> e1 = e.simplify()
         >>> f = Expression('3*4+5')
         >>> f1 = f.simplify()
-        >>> Expression.develop_steps([e1, f1, op.add])
+        >>> dev_steps = Expression.develop_steps([e1, f1, op.add])
+        >>> dev_steps
         [< Step [1, 2, +, 3, 4, *, 5, +, +]>, < Step [3, 12, 5, +, +]>, < Step [3, 17, +]>]
+        >>> for i in dev_steps:
+        ...    print(i)
+        1 + 2 + 3 \times 4 + 5
+        3 + 12 + 5
+        3 + 17
         >>> e = Expression('1+2')
         >>> e1 = e.simplify()
         >>> f = Expression('3*4+5')

pymath/calculus/renderable.py

@@ -76,6 +76,14 @@ class Renderable(object):
         """
         self.postfix_tokens = pstf_tokens
 
+    def __str__(self):
+        """
+        Overload str
+
+        If you want to changer render use Expression.set_render(...) or use tmp_render context manager.
+        """
+        return self.STR_RENDER(self.postfix_tokens)
+
     def __repr__(self):
         return  "< {cls} {pstf_tokens}>".format(
                 cls = str(self.__class__).split('.')[-1][:-2],

pymath/calculus/step.py

@@ -26,7 +26,7 @@ class Step(Renderable):
         \\frac{ 6 }{ 5 }
         >>> with Step.tmp_render():
         ...     for i in exp.simplify().explain():
-        ...         print(i)
+        ...         print(repr(i))
         < Step [2, 3, 5, /, *]>
         < Step [3, 5, /, 2, *]>
         < Step [3, 2, *, 5, /]>