Private Variables and Methods in Python

Question

Possible Duplicate    The meaning of a single- and a double-underscore before an object name in Python       Which should I use  foo  an underscore  or   bar  double underscore  for private members and methods in Python

User · Answer

Double underscore  That mangles the name  The variable can still be accessed  but it s generally a bad idea to do so   Use single underscores for semi-private  tells python developers  only change this if you absolutely must   and doubles for fully private

User · Answer

The double underscore  It mangles the name in such a way that it can t be accessed simply through   fieldName from outside the class  which is what you want to begin with if they re to be private   Though it s still not very hard to access the field    class Foo      def   init   self           self   privateField   4          print self   privateField   yields 4 no problem  foo   Foo   foo   privateField   AttributeError  Foo instance has no attribute    privateField    It will be accessible through  Foo  privateField instead  But it screams  I M PRIVATE DON T TOUCH ME   which is better than nothing

User · Answer

Because thats coding convention  See here for more

User · Answer

Please note that there is no such thing as  quot private method quot  in Python  Double underscore is just name mangling   gt  gt  gt  class A object           def   foo self               pass       gt  gt  gt  a   A    gt  gt  gt  A   dict   keys       dict       A  foo      module        weakref        doc      gt  gt  gt  a  A  foo    So therefore    prefix is useful when you need the mangling to occur  for example to not clash with names up or below inheritance chain  For other uses  single underscore would be better  IMHO  EDIT  regarding confusion on     PEP-8 is quite clear on that   If your class is intended to be subclassed  and you have attributes that you do not want subclasses to use  consider naming them with double leading underscores and no trailing underscores   This invokes Python s name mangling algorithm  where the name of the class is mangled into the attribute name  This helps avoid attribute name collisions should subclasses inadvertently contain attributes with the same name  Note 3  Not everyone likes name mangling   Try to balance the need to avoid accidental name clashes with potential use by advanced callers   So if you don t expect subclass to accidentally re-define own method with same name  don t use it

[python] Private Variables and Methods in Python

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