10.5 Simulating “Private” Attributes

  • Python programmers often use “private” attributes for data or utility methods that are essential to a class’s inner workings but are not part of the class’s public interface
  • Two leading underscores indicates that an attribute (like __hour) or method is “private” and should not be accessible to the class’s clients
  • Python renames such identifiers by preceding the attribute name with ClassName, as in _Time__hour
    • called name mangling

IPython Auto-Completion Shows Only “Public” Attributes

  • IPython does not show attributes with one or two leading underscores when you try to auto-complete an expression by pressing Tab

Demonstrating “Private” Attributes

# private.py
"""Class with public and private attributes."""

class PrivateClass:
    """Class with public and private attributes."""

    def __init__(self):
        """Initialize the public and private attributes."""
        self.public_data = "public"  # public attribute
        self.__private_data = "private"  # private attribute
  • Create an object of class PrivateData
In [1]:
from private import PrivateClass
In [2]:
my_object = PrivateClass()
  • Access the public_data attribute directly
In [3]:
my_object.public_data
Out[3]:
'public'
  • Attempt to access __private_data directly
In [4]:
my_object.__private_data

------------------------------------------------------------------------
AttributeError                         Traceback (most recent call last)
<ipython-input-4-d896bfdf2053> in <module>
----> 1 my_object.__private_data

AttributeError: 'PrivateClass' object has no attribute '__private_data'

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