python-内置常量

>>> True
True
>>> type(True)
<class 'bool'>

>>> True = 1
  File "<stdin>", line 1
SyntaxError: can't assign to keyword

>>> False
False
>>> type(False)
<class 'bool'>

>>> False = 0
  File "<stdin>", line 1
SyntaxError: can't assign to keyword

>>> None
>>> type(None)
<class 'NoneType'>

>>> None = 1
  File "<stdin>", line 1
SyntaxError: can't assign to keyword

>>> def sayhello():  #定义函数
...     print('hello world')
... 
>>> 
>>> sayhello()
hello world
>>> ret = sayhello()
hello world
>>> print(ret)
None
>>> 

>>> NotImplemented
NotImplemented
>>> type(NotImplemented)
<class 'NotImplementedType'>

>>> bool(NotImplemented)
True

>>> bool(NotImplemented)
True
>>> NotImplemented = False

class A(object):
    def __init__(self,name,value):
        self.name  = name
        self.value = value
    def __eq__(self, other):
        print('self:',self.name,self.value)
        print('other:',other.name,other.value)
        return self.value == other.value  #判断两个对象的value值是否相等
a1 = A('Tome',1)
a2 = A('Jim',1)
print(a1 == a2)
#输出
#self: Tome 1
#other: Jim 1
#True

class A(object):
    def __init__(self,name,value):
        self.name  = name
        self.value = value
    def __eq__(self, other):
        print('self:',self.name,self.value)
        print('other:',other.name,other.value)
        return NotImplemented
a1 = A('Tome',1)
a2 = A('Jim',1)
print(a1 == a2)
#输出
# self: Tome 1
# other: Jim 1
# self: Jim 1
# other: Tome 1
# False

>>> Ellipsis
Ellipsis
>>> type(Ellipsis)
<class 'ellipsis'>
>>> ...
Ellipsis
>>> ... == Ellipsis
True

>>> bool(Ellipsis)
True

>>> bool(Ellipsis)
True
>>> Ellipsis = False
>>> bool(Ellipsis)
False

>>> a = [1,2,3,4]
>>> a.append(a)
>>> a
[1, 2, 3, 4, [...]]
>>> len(a)
5
>>> a[4]
[1, 2, 3, 4, [...]]
>>> a[4][4]
[1, 2, 3, 4, [...]]

>>> __debug__
True
>>> type(__debug__)
<class 'bool'>

>>> __debug__ = False
  File "<stdin>", line 1
SyntaxError: assignment to keyword