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From: ram@zedat.fu-berlin.de (Stefan Ram)
Newsgroups: comp.lang.python
Subject: Re: Is Lexical Binding The Norm Yet?
Date: 21 Jan 2024 17:27:09 GMT
Organization: Stefan Ram
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Expires: 1 Dec 2024 11:59:58 GMT
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ram@zedat.fu-berlin.de (Stefan Ram) writes:
>What do you mean, the cloning part is missing?

  Most standard functions do not call the custom dunder methods
  of our prototype-based objects. Yes, the standard library was
  written for class-based objects ("3.3.12 Special method lookup")!

  However, if you just need few staples such as "str" and "print",
  you can define them yourself. (The standard library will not
  use them, but you can call them in your own code.)

import types

# a custom global str functions for prototype objects
# used below
def str( x ): return x.__str__()

# a custom global print functions for prototype objects
# used below
std_print = print
def print( *args, **kwargs ):
    return std_print( *( arg.__str__() for arg in args ), **kwargs )

# create a new object
def counter_object(): pass

# attach a numeric field to the object
counter_object.counter_value = 0

# define a named function
def increment_value( self ): self.counter_value += 1

# attach the named function to the object as a method
counter_object.increment_value = \
types.MethodType( increment_value, counter_object )

# call the method
counter_object.increment_value()

# attach an unnamed function to the object
counter_object.get_value = \
types.MethodType( lambda self: self.counter_value, counter_object )

# attach an unnamed function to the object
counter_object.__str__ = \
types.MethodType\
( lambda self: str( self.counter_value ), counter_object )

# call that method
# Prints "1".
print( counter_object.get_value() )

# An ad-hoc function to clone an object for the purpose of "prototype
# inheritance". Might need to be refined for more general uses.
def clone_object( object_ ):
    def new_object(): pass
    for attribute in dir( object_ ):
        if attribute[ :2 ]!= '__' or attribute in[ '__str__' ]:
            if type( getattr( object_, attribute ))== types.MethodType:
                method = getattr( object_, attribute )
                function = types.FunctionType\
                ( method.__code__, globals() )
                method = types.MethodType( function, new_object )
                setattr( new_object, attribute, method )
            else:
                field = getattr( object_, attribute )
                setattr( new_object, attribute, field )
    return new_object

# create two "clones" ("clone objects")
clone = clone_object( counter_object )
other = clone_object( counter_object )

# The clones "inherited" the counter field including its value.
# Prints "1 1 1".
print( counter_object.get_value(), clone.get_value(), other.get_value() )

# Each object's counter has a value independent from the other
# object's counter.
other.increment_value()

# Prints "1 1 2"
print( counter_object.get_value(), clone.get_value(), other.get_value() )

# Prints "1 1 2"
print( str( counter_object ), str( clone ), str( other ))

# Prints "1 1 2"
print( counter_object, clone, other )