Generator, yield and yield from

yield

variable = yield value

variable is assigned by gen.send()

yield expression

A generator expression is a compact generator notation in parentheses: generator_expression = (expression comp_for) A generator expression yields a new generator object. Its syntax is the same as for comprehensions, except that it is enclosed in parentheses instead of brackets or curly braces.

yield from

The true name of yield from is for loop. It allows the user to delegate tasks to another generator. Additionally, the subgenerator is allowed to return with a value, and the value is made available to the delegating generator. example:

def gen1():
    for i in range(10):
        yield i

gen2 = lambda: (i for i in range(10,20))

def gen():
    for i in gen1():
        yield i
    for i in gen2():
        yield i

>>> list(gen())
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

def gen():
    yield from gen1()
    yield from gen2()

>>> list(gen())
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

lamyield = lambda: (x for x in range(15))
>>> print(*lamyield())
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Even yield from designed to yield from another generator, however, it allows any iterator, example:

def g(x):
    yield from range(x, 0, -1)
    yield from range(x)

>>> list(g(5))
[5, 4, 3, 2, 1, 0, 1, 2, 3, 4]