SymPy IPython Printer trick

SymPyIPythonPrinterTric.py

from sympy import *

class DefinitionSet():
    def __init__(self):
      self.__dict__["__dict2__"]={} # for not fully bound ones --> __getattr__
      
    def __setattr__(self, name, value):
      if name in self.__dict__ or name in self.__dict2__:
        raise TypeError("Immutable: attribute \"%s\" exists"%name)
      else:
        s=self.subs(value)
        if(value!=s):
          display(Eq(Symbol(name),Eq(value,s,evaluate=False),evaluate=False))
        else:
          display(Eq(Symbol(name),value,evaluate=False))

        if(isinstance(s, Expr) and bool(s.free_symbols)):
          self.__dict2__[name]=s
        else:
          self.__dict__[name]=s

    def __getattr__(self,name):
       if name in self.__dict2__:
         s=self.subs(self.__dict2__[name])
         if(s!=self.__dict2__[name]):
           display(Eq(Symbol(name),Eq(self.__dict2__[name],s,evaluate=False),evaluate=False))
           self.__dict__[name]=s
           del(self.__dict2__[name])
         return(s)
       else: 
          return Symbol(name)
    
    def subs(self,exp):
      ret=exp
      if(isinstance(exp, Expr)):
        for i in ret.free_symbols:
          if(i.name in self.__dict__): 
            ret=ret.subs(i,self.__dict__[i.name])
          if(i.name in self.__dict2__):
            ret=ret.subs(i,self.__getattr__(i.name)) 
      return ret

class Symbolizer:
   """create symbols on the fly!?"""
   def __setattr__(self, name, value):
       raise TypeError("Use DefinitionSet to set \"%s\""%name)

   def __getattr__(self,name):
      return Symbol(name)
   

%config InteractiveShell.ast_node_interactivity="none"


ß = DefinitionSet()
ẞ = Symbolizer()

ß.     a=1
ß.     b=sqrt(ẞ.a*ẞ.f)
ß.     f=2
ß.     a_2=ẞ.b