How to join two generators in Python?

I want to change the following code

for directory, dirs, files in os.walk(directory_1):
    do_something()

for directory, dirs, files in os.walk(directory_2):
    do_something()

to this code:

for directory, dirs, files in os.walk(directory_1) + os.walk(directory_2):
    do_something()

I get the error:

unsupported operand type(s) for +: 'generator' and 'generator'

How to join two generators in Python?

Solution 1:

itertools.chain() should do it.

It takes a list of iterables and yields from each one by one

def chain(*iterables):
    for it in iterables:
        for element in it:
            yield element

Usage example:

from itertools import chain
generator = chain('ABC', 'DEF')

for item in generator:
    print(item)

Output:

A
B
C
D
E
F

Solution 2:

A example of code:

from itertools import chain

def generator1():
    for item in 'abcdef':
        yield item

def generator2():
    for item in '123456':
        yield item

generator3 = chain(generator1(), generator2())
for item in generator3:
    print item

Solution 3:

In Python (3.5 or greater) you can do:

def concat(a, b):
    yield from a
    yield from b

Solution 4:

Simple example:

from itertools import chain
x = iter([1,2,3])      #Create Generator Object (listiterator)
y = iter([3,4,5])      #another one
result = chain(x, y)   #Chained x and y

Solution 5:

With itertools.chain.from_iterable you can do things like:

def genny(start):
  for x in range(start, start+3):
    yield x

y = [1, 2]
ab = [o for o in itertools.chain.from_iterable(genny(x) for x in y)]
print(ab)