Lecture#3
.pdf
Classes inheritance
class Primitive(object): 
field = 5.
def get_field(self):
return self.field
class NewPrimitive(Primitive): 
def get_field(self):
print self.field 
return self.field
Classes inheritance
NewPrimitive can be used instead of Primitive
Child classes can
add functionality to parent class change functionality of parent class
NewPrimitive is Primitive
Classes
multiple inheritance
class Primitive(object): 
field = 5.
class AnotherPrimitive(object): 
anotherfield = 10.
class Derived(Primitive, AnotherPrimitive): 
def get_fields(self):
print field
print anotherfield
Classes
multiple inheritance
No conflicts - no problems
Classes polymorphism
class LinearAccelerator(object): 
def collide(self):
print “I use steady target” class Collider(object):
def collide(self):
print “I use two beams”
Both can collide. But differently.
Classes encapsulation
Refer to:
hiding data inside classes (i.e. private methods and attrs)
bundling data and operations on it inside classes
Classes encapsulation
class Cl(object):
_field = 5. #indicates “for internal use” 
__priv = 10. #magled, i.e. __Cl_priv
Encapsulation is mostly bundling in Python
Classes composition
class P(object):
pass
class R(object):
def set_P(self, P): 
self.P = P
R “has” or “is composed of” P
Modules
A way to structure code #a.py:
class P(object): 
pass
#b.py import a p = a.P()
Modules import syntax
import <module>
import <module> as <newname>
from <module> import <name1>, <name2> from <module> import *
from <module> import <name> as <name2>