Recursive method in class
ast
none at gmail.com
Tue Oct 1 03:37:16 EDT 2019
Le 30/09/2019 à 13:11, Anders Märak Leffler a écrit :
> What do you mean by transformed? This is probably your understanding
> already, but a further consequence of when arguments are evaluated
> plus what you said about data attributes is that the fib(self, n - 1)
> call will follow the standard LEGB-lookup of whatever "fib" is, from
> the point of view of the function object. As far as I know, there is
> no transformation of these scopes - either when it comes to creating
> the class, or creating the instances. (self is just the instance,
> passed as an argument.)
>
> Cf when you change a binding:
>
>>>> def factorial(self, n):
> ... if not n:
> ... return 1
> ... else:
> ... return n * factorial(self, n - 1)
> ...
>>>> Dummy = type("DummyObject", (object, ), {"factorial" : factorial})
>>>> instance = Dummy()
>>>> def factorial(self, n):
> ... print("Hello!")
> ... return 999
> ...
>>>> instance.factorial(5) # Where will the call go ("old" or "new" factorial?)? Where will possible recursive calls go (and why)?
> Hello!
> 4995
>
> Oh, and as others have pointed out on this list - you/whoever runs the
> system sending the mail might want to change the return address.
> none at gmail.com is somewhat consistently classed as spam.
>
>
>
> //Anders
>
> PS. We could further complicate this by adding a call to
> self.factorial in the new function, but let's not go there. :)
>
I understood your example, but it doesn't answer my initial question.
I try to rewrite my question:
The following code is working well and I don't really understand why
def factorial(self, n):
if not n:
return 1
else:
return n * factorial(self, n - 1)
Dummy = type("DummyObject", (object, ), {"factorial" : factorial})
instance = Dummy()
instance.factorial(3)
6 # correct
The problem is that "factorial" in line
"return n * factorial(self, n - 1)" should not have been found
because there is no factorial function defined in the current
scope.
if you use "class" keyword to define the class
class Dummy:
def factorial(self, n):
if not n:
return 1
else:
return n * factorial(self, n - 1)
instance = Dummy()
instance.factorial(3)
It generate an error because "factorial" in line
"return n * factorial(self, n - 1)" is not found.
Traceback (most recent call last):
File "<pyshell#42>", line 1, in <module>
instance.factorial(3)
File "<pyshell#40>", line 7, in factorial
return n * factorial(self, n - 1)
NameError: name 'factorial' is not defined
This is OK to me
The correct way is to write:
class Dummy:
def factorial(self, n):
if not n:
return 1
else:
return n * self.factorial(n - 1)
instance = Dummy()
instance.factorial(3)
6 # correct
So, to summarize, if you create a class with type(name, bases, dict_)
or with the "class" keyword, recursive methods can't be writen
in the same way. This is what puzzle me.
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