Public and private methods in Python [duplicate]

I'm assuming that by using terms such as struct, public and private you must come from a background of C/C++. There are no such things in Python, and the naming of the attributes are purely conventional.

I recommend reading What is the meaning of a single and a double underscore before an object name?.

Typically for your "private" attributes which you don't want for others to use outside of your class, the convention is to prefix it with a single underscore _, like _size. If you plan on using this outside, it boils down to these cases:

• do you want it to be writable from outside? In that case you just define it as size and use it like this everywhere
• do you want it to be read-only from outside? In this case you can make it private and make a property for it like:

Code:

class A:

    self __init__(self, size):
        self._size = size

    @property
    def size(self):
        return self._size

You also have the ability to translate the internal variable to another name, and make it writable at the same time under that different name.

Example:

class A:

    def __init__(self, value):
        self._internal_var = value

    def set_data(self, value):
        self._internal_var = value

    def get_data(self):
        return self._internal_var

    data = property(get_data, set_data)

Or alternatively:

@property
def data(self):
    return self._internal_var

@data.setter
def data(self, value):
    self._internal_var = value

Then if you call

a1 = A(11)
print(a1.data)
a1.data = 22
print(a1.data)

it will yield:

11
22