python - Confusion about global and immutable -


i'm confused global , immutable variable. have code:

class processobject:     rr = 0     def b(self):         self.rr=5         print("valor: ", self.rr)      def c(self):         print("final: ", self.rr)      def d(self):         global rr         rr = 3         print("valor: ", rr)      print(rr)  proce = processobject() proce.b() proce.c() proce.d() proce.c()

and have output:

0 value:  5 final:  5 value:  3 final:  5

but not understand why "c" value 5 if rr object immutable. , why "d" using global no mute value of rr.

this has nothing immutability... anyway:

class processobject:     # "rr" lives in `class` statement namespace,      # it's accessible 'rr' in namespace. after     # `class` statement executed, becomes attribute     # of `processobject` class, accessible `processobject.rr`,     # , thru instances `processobject().rr`.      #       rr = 0      def b(self):         # creates "rr" instance attribute         # on current instance (`self`), shadows         # "rr" class attribute         self.rr=5         print("valor: ", self.rr)      def c(self):         print("final: ", self.rr)      def d(self):         # 2 following lines creates module-global         # name "rr", distinct 2 previous         # ones.           global rr         rr = 3         print("valor: ", rr)      # prints value of `rr` living in class     # statement scope - not value of yet non-existing     # global rr     print(rr)  proce = processobject() proce.b() # creates `proce.rr` instance attribute proce.c() proce.d() proce.c()

but not understand why "c" value 5 if rr object immutable.

it prints '5' because assigned value proce.rr when calling proce.b(). you're confusing names , values... rr not object, it's name bound object. fact it's @ 1 point bound immutable object doesn't mean cannot rebind object (mutable or not, that's irrelevant here).

and why "d" using global no mute value of rr

and here confusing binding (assignment) , mutating. binding (assignment) means "make name points object", mutating means "change state of object". example of mutation adding or removing element to/from list, or reversing list in place.

fwiw, call proce.d rebind (and bind on first call) module-global "rr".

you may want run '"extended" version of script find out happens:

print("before : globals = {}".format(globals()))  class processobject:     rr = 0     print "rr defined in class namespace - not in globals: {}".format(globals())      def __init__(self):         print("in init")         print("   self.__dict__ : {}".format(self.__dict__))         print("   processobject.__dict__ : {}".format(processobject.__dict__))        def b(self):         print("before calling b - self.__dict__ : {}".format(self.__dict__))         self.rr=5         print("valor: ", self.rr)         print("after calling b - self.__dict__ : {}".format(self.__dict__))      def c(self):         print("before calling c - self.__dict__ : {}".format(self.__dict__))         print("final: ", self.rr)      def d(self):         print("before calling d : globals = {}".format(globals()))         global rr         rr = 3         print("valor: ", rr)         print("after calling d : globals = {}".format(globals()))      print(rr)  print("after class statement: globals : {}".format(globals()))    proce = processobject() proce.c() proce.b() proce.c() proce.d() proce.c()

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