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Python Object
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Stephen Finucane
July 12, 2016
Technology
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Python Object
How objects work in Python. A talk I gave to OSIC members, October 2015.
Stephen Finucane
July 12, 2016
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Transcript
Stephen Finucane Software Developer, OpenStack Team Intel Shannon
What is Object Orientated design, and why do we care?
What is an object?
Know Java, and know Python is not Java These slides
compare the two, assuming Java knowledge for fair comparison. Don’t try to write Python like Java, though.
None
class MyClass(object): def __init__(self, *args, **kwargs): pass def do_stuff(self): print('doing
stuff') >> instance = MyClass() >> instance.do_stuff() doing stuff classes.py: An example of classes in Python
class MyClass(object): def __init__(self, *args, **kwargs): pass def do_stuff(self): print('doing
stuff')
object is Python being explicit You don’t need it in
Python 2, but you should use it to get “new style classes”
self is also Python being explicit Think of it like
the ‘this’ keyword in Java
public class MyClass { String name; ... public void setName(String
name) { this.name = name; } } MyClass.java: The ‘this’ keyword
class MyClass(object): name = None ... def set_name(self, name): self.name
= name self._example.py: The ‘self’ keyword
None
public class MyClass { public MyClass(String name) { ... }
public MyClass(String name, int age) { ... } } MyClass.java: Constructors in Java
class MyClass(object): def __init__(name, age=None): ... constructors.py: Constructors in Python
public class MyClass { public void display() { System.out.println("Hello, world!");
} } public class MySubClass extends MyClass { public void display() { System.out.println("Testing 123"); } } MyClass.java, MySubClass.java: Inheritance in Java
class MyClass(object) { def display(self): print('Hello world') class MySubClass(MyClass): def
display(self): print('Testing 123') constructors.py: Constructors in Python
public class MySubClass extends MyClass { public void display() {
super.display(); System.out.println("Testing 123"); } } MyClass.java, MySubClass.java: Inheritance in Java
class MySubClass(MyClass): def display(self): super(MySubClass, self).display(self) print('Testing 123') superclasses.py: Accessing
the Super Class
None
public interface Animal { public void eat(); public void travel();
} public class Mammal implements Animal { public void eat() { System.out.println("Mammal eats"); ... Animal.java, Mammal.java: Interfaces in Java
class Mammal: def eat(self): print('Mammal eats') ... class Reptile: def
eat(self): print('Reptile eats') ... animals.py: Duck Typing in Python
None
>> stephens_boat = Boat(...) >> ankurs_boat = Boat(...) >> stephens_boat
> ankurs_boat True The data model in practice
class Boat(object): """Model a boat.""" length = 0 color =
None def __init__(self, length, color): ... def __gt__(self, other): return self.length > other.length: boat.py: Using the data model
__lt__ - less than __le__ - less than or equal
__eq__ - equal __ne__ - not equal __gt__ - greater than __ge__ - greater than or equal __cmp__ - fallback, if above not implemented boat.py: Using the data model
>>> stephens_boat = Boat(100, 'red') >>> stephens_boat.__doc__ Model a boat.
>>> stephens_boat.__dict__ {'color': 'red', 'length': 100} >>> stephens_boat.__class__ <class '__main__.Boat'> The data model in practice
None
class Person(object): weight_kg = 0 @property def weight_lb(self): return self.weight_kg
* 2.2 @weight_lb.setter def weight_lb(self, value): self.weight_kg = value / 2.2 boat.py: Using the data model
None
• https://docs.python.org/2/tutorial/classes.html • https://en.wikipedia.org/wiki/Duck_typing • https://stackoverflow.com/questions/222877/how-to-use-super- in-python • https://docs.python.org/2/reference/datamodel.html