FAQ: Graphs: Python - Finding a Path II


This community-built FAQ covers the “Finding a Path II” exercise from the lesson “Graphs: Python”.

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This exercise can be found in the following Codecademy content:

Computer Science

Complex Data Structures

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It says to use the .extend() method in the fourth instruction and I don’t think I’ve been introduced to that before so I had no way to know to use that. I looked through all the code to try to find the .extend() method to no avail, so now i’m here asking what it’s about.



I know its been a while since you asked, but since i stumbled with the lesson today, i’m gonna give an answer.

Python commands and functions are way bigger than Codecademy lessons. You need to use other sources to feed your curiosity. I knew about .extend() because of that, it was my first choice. There is another option += that is also valid, but for some reason i forget that it works with lists too (i use it mostly with counter variables).


I am going to have to grab the solution to move to the next step…as I cannot see what is wrong with the above…you can see the error.

No doubt but that it is something simple…

P.S. I can add that by not scrolling I missed adding the return when I tried running the change.

i.e. I went into the error state…but adding the return and re-running failed to clear the matter.

Thank you!

Hello mate, maybe they want you to use .extend() list method instead using +=

TL;DR: They are semantically similar, but not the same for any case.

.extend would do the trick. Remember that it’s an automated checking. Regarding .extend you can read the Python 3 doc https://docs.python.org/3/tutorial/datastructures.html

It’s important to note, that while in this case start += next_vertices would behave equal to start.extend(next_vertices) the fact is that although being “semantically” similar, the += would not work if there were something like a tuple (inmutable) involved, or more precise, if the list were an attribute of a inmutable object, while extend would work (see picture).

I hope it helps…

1 Like

An excellent point. (the screenshot tells it all) Thank you!