self.python vs Current.eiffel

[Egbert Bouwman]

In a python method the following instruction is allowed:
   self.x = self.x + a
On page 187 of OOSC, Meyer seems to say that in Eiffel you cannot say:
   Current.x := Current.x + a   
He says:  ...the occurrence of x on the left is not an expression
(one cannot assign a value to an expression), so it would be 
meaningless to replace it by Current.x

I am lost. What are the differences between python's self and x,
and Eiffel's Current and x ?
egbert
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