In [1]:

    

import collections


    

In [2]:

    

def print_len_abc_sized(x):
    if isinstance(x, collections.abc.Sized):
        print(len(x))
    else:
        print('x is not Sized')


    

In [3]:

    

print_len_abc_sized([0, 1, 2])


    

    




3

In [4]:

    

print_len_abc_sized('abc')


    

    




3

In [5]:

    

print_len_abc_sized({0, 1, 2})


    

    




3

In [6]:

    

print_len_abc_sized(100)


    

    




x is not Sized

In [7]:

    

def print_len_abc_sequence(x):
    if isinstance(x, collections.abc.Sequence):
        print(len(x))
    else:
        print('x is not Sequence')


    

In [8]:

    

print_len_abc_sequence([0, 1, 2])


    

    




3

In [9]:

    

print_len_abc_sequence('abc')


    

    




3

In [10]:

    

print_len_abc_sequence({0, 1, 2})


    

    




x is not Sequence

In [11]:

    

print_len_abc_sequence({'k1': 1, 'k2': 2, 'k3': 3})


    

    




x is not Sequence

In [12]:

    

def print_len_abc_mutablesequence(x):
    if isinstance(x, collections.abc.MutableSequence):
        print(len(x))
    else:
        print('x is not MutableSequence')


    

In [13]:

    

print_len_abc_mutablesequence([0, 1, 2])


    

    




3

In [14]:

    

print_len_abc_mutablesequence('abc')


    

    




x is not MutableSequence

In [15]:

    

print_len_abc_mutablesequence((0, 1, 2))


    

    




x is not MutableSequence

In [16]:

    

class MySequence(collections.abc.Sequence):
    def __len__(self):
        return 10


    

In [17]:

    

# ms = MySequence()
# TypeError: Can't instantiate abstract class MySequence with abstract methods __getitem__


    

In [18]:

    

class MySequence(collections.abc.Sequence):
    def __len__(self):
        return 10
    def __getitem__(self, i):
        return i


    

In [19]:

    

ms = MySequence()


    

In [20]:

    

print(len(ms))


    

    




10

In [21]:

    

print(ms[3])


    

    




3

In [22]:

    

print(ms.index(5))


    

    




5

In [23]:

    

print(list(reversed(ms)))


    

    




[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

In [24]:

    

print(isinstance(ms, collections.abc.Sequence))


    

    




True

In [25]:

    

print(hasattr(ms, '__len__'))


    

    




True

In [26]:

    

class MySequence_bare():
    def __len__(self):
        return 10

    def __getitem__(self, i):
        return i


    

In [27]:

    

msb = MySequence_bare()


    

In [28]:

    

print(len(msb))


    

    




10

In [29]:

    

print(msb[3])


    

    




3

In [30]:

    

# print(msb.index(5))
# AttributeError: 'MySequence_bare' object has no attribute 'index'


    

In [31]:

    

print(isinstance(msb, collections.abc.Sequence))


    

    




False

In [32]:

    

print(hasattr(msb, '__len__'))


    

    




True