Nested objects in Python

Question

I am realizing a porting from Java to Python. Now, I would like to define an object by using another one as neested attribute.

To be clear, taking into account the Java code as follows:

public class Foo {

    private String fooName;

    public Foo(String fooName) {
        setFooName(fooName);
    }

    public void setFooName(String fooName) {
        this.fooName = fooName;
    }

    public String getFooName() {
        return this.fooName;
    }

}

public class Bar {

    private String barName;
    private Foo foo;

    public Bar(String barName, Foo foo) {
        setBoName(fooName);
        setFoo(foo);
    }

    public void setBarName(String barName) {
        this.barName = barName;
    }

    public String getBarName() {
        return this.barName;
    }

    public void setFoo(Foo foo) {
        this.foo = foo;
    }

    public Foo getFoo() {
        return this.foo;
    }

}

How can I do just the same in Python?

Cory Kramer · Accepted Answer · 2015-06-12 14:12:48Z

7

Your classes would be as follows, note that there is no notion of public vs private so you do not need setters and getters

class Foo:
    def __init__(self, fooName):
        self.fooName = fooName

class Bar:
    def __init__(self, barName, foo):
        self.barName = barName
        self.foo = foo

As an example

>>> f = Foo('bob')
>>> b = Bar('steve', f)
>>> f.fooName
'bob'
>>> b.barName
'steve'
>>> b.foo
<__main__.Foo object at 0x02F93070>
>>> b.foo.fooName
'bob'

Again I would like to stress that the general use of setters and getters is not considered Pythonic. Either don't write/use them, or if the need arises, use @property decorators instead

edited Jun 12, 2015 at 14:12

answered Jun 12, 2015 at 13:41

Cory Kramer

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Comments

user142650 · Accepted Answer · 2015-06-12 13:45:08Z

Python syntax is a bit different. It will help a lot more if you read up a bit before diving deep into it. A few things that you must take into account are:

Data types
Private/public fields/functions - pythonic way of 'suggesting' them
Brackets, semicolons are not considered good

But here's a demo:

class Foo(object):
    def __init__(self, fooName):
        self.setFooName(fooName)

    def setFooName(self, fooName):
        self._fooName = fooName

    def getFooName(self):
        return self._fooName

class Bar(object):
    def __init__(self, barName, foo):
        self.setBoName(fooName)
        self.setFoo(foo)

    def setBarName(self, barName):
        self._barName = barName

    def getBarName(self):
        return self._barName

    def setFoo(self, foo):
        self._foo = foo

    def getFoo(self):
        return self._foo

Thomas Weglinski · Accepted Answer · 2015-06-12 13:58:23Z

From the Python documentation:

There is a convention that is followed by most Python codes: a name prefixed with an underscore (e.g. _spam) should be treated as a non-public part of the API (whether it is a function, a method or a data member).

See: https://docs.python.org/2/tutorial/classes.html#private-variables-and-class-local-references for more details.

As Java-based classes often "hidden" their fields (by making it private) and provides public getters/setters for this fields, you may achieve this in Python using that convention:

class Foo(object):

    def __init__ (self, fooName):
        self.setFooName(fooName)


    def setFooName(self, fooName):
        self.__fooName = fooName


    def getFooName():
        return self.__fooName;


class Bar(object) :

    def __init__(self, barName, foo) :
        self.setBarName(barName)
        self.setFoo(foo)


    def setBarName(self, barName) :
        self.__barName = barName


    def getBarName(self) :
        return self.__barName

    def setFoo(self, foo) :
        self.__foo = foo;


    def getFoo(self) :
        return self.__foo;


foo = Foo("foo")
bar = Bar("bar", foo)

print bar.getBarName()
print type(bar.getFoo())
# print bar.__barName -> this will return error as the variable is considered "private"

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