2.7 base. It is a prerequisite that you know some other language.
from import Declaration "Use Decimal class from standard module called decimal"
>>> from decimal import Decimal
Import all classes
>>> d = Decimal(10)
>>> print d
10
>>> print d + 3 #Decimal class+Has a method corresponding to the operator
13
For more information about Decimal http://docs.python.jp/2/library/decimal.html
>>> class MyClass:
... pass
...
>>> mc = MyClass()
>>> print mc
<__main__.MyClass instance at 0x1076245a8>
Class names are usually written in camel case. pass is a Null Operation and does nothing.
Python does not have the ability to write member variable definitions along with class definitions. Attributes (data members) are defined for each instance by assigning them to variables separated by dots for the created instance.
>>> mc = MyClass()
>>> mc.value = 10
>>> print(mc.value)
10
>>> mc2 = MyClass()
>>> print mc2.value
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: MyClass instance has no attribute 'value'
\ Init (and \ __ new__) are provided as constructor-like initialization methods.
class MyClass:
#Initialization method
def __init__(self):
self.h = 'hoge' #Add attributes
#Method
def print_h(self):
print h
mc = MyClass()
mc.print_h() # => 'hoge'
The instance object itself is passed to the first argument, self. It is customary to use self, but this and me also work. If you want to give a variable at initialization
class Rect:
def __init__(self, width, height):
self.width = width
self.height = height
def area(self):
return self.width * self.height
r = Rect(100, 50)
print r.height # => 50
print r.area # => 5000
become that way. Note that the caller of the initialization method ignores the first argument. If you forget self as an argument,
>>> class MyClass():
... def hoge():
... print 'hoge'
...
>>> mc = MyClass()
>>> mc.hoge()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: hoge() takes no arguments (1 given)
Will result in the error.
There are no private keywords in python, and if you want to hide an attribute or method name, put an underscore (one or two) in front of it.
def _private_method():
# ....
def __secret_method():
# ....
In one case, it is customary to express the intention to "don't call from the outside", and in the two cases, the name is automatically changed internally to make it uncallable from the outside.
class MyClass:
def __init__(self, size):
self._size = size
self.__size = size
mc = MyClass(100)
print mc._size # => 100
print mc.__size # => AttributeError
Python supports ** multiple inheritance **. You can also create new classes by inheriting built-in types such as numbers and strings.
class
It seems that the behavior is slightly different when the inherited class is not specified and when object is inherited. It is recommended to inherit object if it does not inherit anything (?).
In Python3, it seems that object will be inherited by default if the parent class is not specified.
class C1():
pass
print dir(C1) #=> ['__doc__', '__module__']
class C2(object):
pass
print dir(C2) #=> ['__class__', '__delattr__', '__dict__', '__doc__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__', '__weakref__']
class Rectangle(object):
def __init__(self, w, h):
self.w = w
self.h = h
self.color = 'red'
def area(self):
return self.w * self.h
class Square(Rectangle):
#Redefine (override) initialization method
def __init__(self, length):
self.w = self.h = length
s = Square(100)
print s.area() #=>10000, parent class method call
Method overriding is a complete overriding, and it doesn't act like calling the parent's constructor automatically. So, for example, the variable color initialized by the parent class \ __ init__ () above does not exist in the Square class instance. To prevent that, call the parent method with super (),
class Square(Rectangle):
def __init__(self, length):
super(Square, self).__init__(length, length)
I have to call it awkward. Identify the parent class by passing your type and self. Also, at this time, if the parent class does not inherit the object class, an error will occur.
In Python3, it seems that you can get a superclass with just super ().
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