Python Forum

Hello,

I would like to add every element of a list on every list from a list of lists. Ie :

H = [[1,2],[3,4]]
I = [5,6]

With this result :

Output:
J = [[1,2,5], [3,4,5], [1,2,6], [3,4,6]]

I don’t find the good logic.

Ie :

j = []
for x in h :
	for y in i :
		j.append(h+i)
		print (j)

Gives me :

Output:
[[[1, 2], [3, 4], 5, 6]]
[[[1, 2], [3, 4], 5, 6], [[1, 2], [3, 4], 5, 6]]
[[[1, 2], [3, 4], 5, 6], [[1, 2], [3, 4], 5, 6], [[1, 2], [3, 4], 5, 6]]
[[[1, 2], [3, 4], 5, 6], [[1, 2], [3, 4], 5, 6], [[1, 2], [3, 4], 5, 6], [[1, 2], [3, 4], 5, 6]]

Or again :

k = []
for w in h :
	for z in i :
		o = [w,z]
		k.append(o)
		print (k)

Will give :

Output:
[[[1, 2], 5]]
[[[1, 2], 5], [[1, 2], 6]]
[[[1, 2], 5], [[1, 2], 6], [[3, 4], 5]]
[[[1, 2], 5], [[1, 2], 6], [[3, 4], 5], [[3, 4], 6]]

I’ve tried some tests with map, but nothing conclusive.

Can you help me please to solve my problem ?

My subjective opinion is that 'not finding good logic' starts with bad naming habits. What are H and I? The last name ('I') I would call 'crime against readers of your code', PEP8 Names to avoid:

Quote:Never use the characters 'l' (lowercase letter el), 'O' (uppercase letter oh), or 'I' (uppercase letter eye) as single character variable names.

In some fonts, these characters are indistinguishable from the numerals one and zero. When tempted to use 'l', use 'L' instead.

I add that 'l' and 'I' are also pretty similar to each other.

Now to problem at hand: list comprehension could be suitable tool:

>>> target = [[1,2],[3,4]]
>>> source = [5,6]
>>> [[*item, num] for num in source for item in target]
[[1, 2, 5], [3, 4, 5], [1, 2, 6], [3, 4, 6]]

Hello,

At first, thank you for the edit from the moderator, I had not found how to present it, now I know. Thanks again.

For the letters, thank you. I'm a beginner, I knew that but as it was just an example I've believed it was ok. Sorry, I've noticed and I'll don't do that again.

Now, about the solution, I thank you. Can you give me an explanation with it please ? I search to understand everything.

For what I see, you've added a star in front of item ; is that the way to do what I want ? Have you a link where it's teaching and can you write the long version to help my comprehension ?

On Internet, I can't find an explanation (I've read all the tutorial section on Python documentation, maybe I've jumped something). Item isn't a method which gives a dictionnary ?

Here item is just a word (I've tried your code changing item to be sure), but it a function too no ?

Sorry for my lack of knowledge.

(Mar-28-2020, 08:34 AM)PUP280 Wrote: [ -> ]Can you give me an explanation with it please ?

This is nested list comprehension combined with iterable unpacking.

Documentation > The Python Tutorial > Data Structures > 5. More on Lists > 5.1.3. List Comprehensions

Documentation > The Python Language Reference > 6. Expressions > 6.15. Expression Lists

PEP448 - Additional Unpacking Generalizations

(Mar-24-2020, 10:50 AM)PUP280 Wrote: [ -> ]Or again :

k = []
for w in h :
	for z in i :
		o = [w,z]
		k.append(o)
		print (k)

Will give :

Output:
[[[1, 2], 5]]
[[[1, 2], 5], [[1, 2], 6]]
[[[1, 2], 5], [[1, 2], 6], [[3, 4], 5]]
[[[1, 2], 5], [[1, 2], 6], [[3, 4], 5], [[3, 4], 6]]

I’ve tried some tests with map, but nothing conclusive.

Can you help me please to solve my problem ?

Had you realized, the code is actually right just that the print statement is in the wrong place. It should be :

H = [[1,2],[3,4]]
I = [5,6]
k = []
for w in H :
    for z in I :
        o = [w,z]
        k.append(o)
print (k)

And it gives output:

Output:
[[[1, 2], 5], [[1, 2], 6], [[3, 4], 5], [[3, 4], 6]]

Thank you perfringo :)