Edit - Stack Overflow

You are not logged in. Your edit will be placed in a queue until it is peer reviewed.

We welcome edits that make the post easier to understand and more valuable for readers. Because community members review edits, please try to make the post substantially better than how you found it, for example, by fixing grammar or adding additional resources and hyperlinks.

Required fields*

Rev

Required fields*

Public and private methods in Python [duplicate]

I am trying to change a public to private parameter inside a Python class. As far as I know, to make it private I need to declare for instance:

self.__top = None # <-- Instead of self.top = None

However, I cannot figure out how to make a private struct with private properties, such that they are called properly in the public methods.

For instance:

class Stack:

    def __init__(self, size=None):
        self.__top = None
        if size is None:  # if size is unset
            self.__size = -1
        else:
            self.__size = size
        self.__current_size = -1

    def push(self, data):
        if self.current_size >= self.size: # ERROR!
            print("Stack Overflow!")
            return

Answer*

I'm assuming that by using terms such as *struct*, *public* and *private* you must come from a background of [C][1]/[C++][2]. 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?][3]*.

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

[1]: https://en.wikipedia.org/wiki/C_%28programming_language%29
  [2]: https://en.wikipedia.org/wiki/C%2B%2B
  [3]: https://stackoverflow.com/questions/1301346/what-is-the-meaning-of-a-single-and-a-double-underscore-before-an-object-name

Edit Summary*

Cancel

Add a comment |

Correct minor typos or mistakes
Clarify meaning without changing it
Add related resources or links
Always respect the author’s intent
Don’t use edits to reply to the author

create code fences with backticks ` or tildes ~
```
like so
```
add language identifier to highlight code
```python
def function(foo):
print(foo)
```
put returns between paragraphs
for linebreak add 2 spaces at end
_italic_ or **bold**
indent code by 4 spaces
backtick escapes `like _so_`
quote by placing > at start of line
to make links (use https whenever possible)

<https://example.com>

[example](https://example.com)

<a href="https://example.com">example</a>

formatting help »
answering help »

Collectives™ on Stack Overflow

Public and private methods in Python [duplicate]

Answer*