Python

Iterable is an object, which one can iterate over

from collections.abc import Iterator, Iterable

# List
l = [1, 2, 3, 4, 5, 6]
isinstance(l, Iterable) # True

# Range
r = range(10)
isinstance(r, Iterable) # True

# Tuple
t = (1, 2, 3, 4)
isinstance(t, Iterable) # True

# String
s = 'Hello World!'
isinstance(s, Iterable) # True

# Dict
d = {'x':1, 'y':2}
isinstance(d, Iterable) # True

Iterator is an object, which is used to iterate over an iterable object using __next__() method

# List
l = [1, 2, 3, 4, 5, 6]
obj = iter(l) # list_iterator
isinstance(obj, Iterator) # True

# Range
r = range(10)
obj = iter(r) # range_iterator
isinstance(obj, Iterator) # True

# Tuple
t = (1, 2, 3, 4)
obj = iter(t) # tuple_iterator
isinstance(obj, Iterator) # True

# String
s = 'Hello World!'
obj = iter(s) # str_iterator
isinstance(obj, Iterator) # True

# Dict
d = {'x':1, 'y':2}
obj = iter(d) # dict_keyiterator
isinstance(obj, Iterator) # True

l = [1, 2, 3, 4, 5, 6]
obj = iter(l) # iterator

try:
    while True:
        #if no more element, next raise StopIteration
        item = next(obj) # int
except StopIteration:
    pass

Iterable and iterator are the same object

class yrange:
    def __init__(self, n):
        self.i = 0
        self.n = n
 
    def __iter__(self): # make an object to be iterable
        print('iter')
        self.i = 0
        return self # return an iterator
 
    def __next__(self): # make an object to be iterator
        print('next')
        if self.i < self.n:
            i = self.i
            self.i += 1
            return i
        else:
            raise StopIteration()

y = yrange(10)
isinstance(y, Iterable) # True
isinstance(y, Iterator) # True

# use as an iterable
y = yrange(3)
# call _iter_ to initialize, then call __next__ to iterate
for i in y: # print 0, 1, 2
    print(i)

for i in y: # print 0, 1, 2
    print(i)

# use as an iterator
y = yrange(3)
try:
    # call _next__ to iterate
    while True: # print 0, 1, 2
        temp = next(y) # int
        print(temp)
except StopIteration:
    pass

try:
    while True: # print nothing, iterator has been comsumed
        temp = next(y) # int
        print(temp)
except StopIteration:
    pass

Iterable and iterator are not the same object

# define iterable
class zrange:
    def __init__(self, n):
        self.n = n
 
    def __iter__(self):
        print('iter')
        return zrange_iter(self.n)
 
# define iterator
class zrange_iter:
    def __init__(self, n):
        self.i = 0
        self.n = n
    
    def __next__(self):
        print('next')
        if self.i < self.n:
            i = self.i
            self.i += 1
            return i
        else:
            raise StopIteration()

z = zrange(3)
isinstance(z, Iterable) # True
isinstance(z, Iterator) # False

# used as an iterable
z = zrange(3)
for i in z: # call _iter_ to initialize, then call __next__ to iterate
    print(i)

Generator is iterator, can be consumed in a single iteration

import types

# list
l = [x*x for x in range(4)]; # [0, 1, 4, 9]
print(l)
 
# generator
g = (x*x for x in range(4));
isinstance(g, Iterable) # True
isinstance(g, Iterator) # True
isinstance(g, types.GeneratorType) # True

for i in g: # 0 1 4 9
	print(i)

for i in g: # do nothing, g has been consumed in the above for loop
	print(i)

def grange(n):
    i = 0;
    while i < n:
        yield i;
        i += 1

g = grange(10);

isinstance(g, Iterable) # True
isinstance(g, Iterator) # True
isinstance(g, types.GeneratorType) # True

# use as an iterable
for i in g:
	print(i)
 
for i in g: # do not print anything, g has been consumed
	print(i)

# use as an iterator
try:
    while True: 
        temp = next(g) # int
        print(temp)
except StopIteration:
    pass

try:
    while True: # print nothing, iterator has been comsumed
        temp = next(g) # int
        print(temp)
except StopIteration:
    pass

import sys

# list, iterable
l = [x*x for x in range(100)]
sys. getsizeof(l) # 920

# list iterator
obj = iter(l)
sys. getsizeof(obj) # 48

# generator, iterable, iterator
g = (x*x for x in range(100))
sys. getsizeof(g) # 112

obj = iter(g)
sys. getsizeof(obj) # 112

# range, iterable
r = range(100)
sys. getsizeof(r) # 48

obj = iter(r)
sys. getsizeof(obj) # 48