Concatenate while yielding

Question

How can I concatenate two items when yielding from a function in python?

The base case:

import itertools

def test():
    for number in range(0,10):
        yield number

list(test()) # [0...9]

What if I want to yield both the number and its square number**2

import itertools

def test():
    for number in range(0,10):
        yield itertools.chain.from_iterable([
            number,number*2
        ])

list(test()) 

# [0,0,1,1,2,4,3,9,...] pretended
# <itertools.chain at 0x135decfd0> ... what I got

However doing itertools.chain.from_iterable([generator1, generator2]) from the outside gives the expected result.

def first_list():
    for number in range(0,5):
        yield number

def second_list():
    for number in range(5,10):
        yield number

list(itertools.chain.from_iterable([first_list(), second_list()]))

You don't want to concatenate, you want a double yield ... that's a difference. — Paebbels, May 10 '17 at 23:25

score 11 · Answer 1 · answered May 10 '17 at 22:23

Python 3.3 also introduced the yield from (see also PEP-380) syntax which allows you to do something like this:

>>> def test():
...   for number in range(10):
...     yield from (number, number**2)
...
>>> list(test())
[0, 0, 1, 1, 2, 4, 3, 9, 4, 16, 5, 25, 6, 36, 7, 49, 8, 64, 9, 81]

carlos rodrigues · Accepted Answer · 2017-05-12T14:10:24.517

10

A simple way is:

def test():
    for number in range(0,10):
        yield number 
        yield number**2

edited May 12 '17 at 14:10

answered May 10 '17 at 22:18

carlos rodrigues

317
5
12

Concatenate while yielding

2 Answers2