Nesting if clauses vs cascade return vs assertion

When negative evaluation in if clause will cause a return call inside a function/method, what is more recommended in Python, to nest the if clauses or to utilise the inverse evaluation and call the function return? e.g.:

if required_condition_1:
    if required_condition_2:
        if required_condition 3:
            pass
        return 'error for condition 3'
    return 'error for condition 2'
return 'error for condition 1'

Or:

if not required_condition_1:
    # preparation...
    return 'error for condition 1'

if not required_condition_2:
    # preparation...
    return 'error for condition 2'

if not required_condition_3:
    # preparation...
    return 'error for condition 3'

# if runtime reaches this point it means that it has passed all conditions

I have also thought about assertion:

try:
    assert(required_condition_1)
    try:
        assert(required_condition_2)
        # do tasks
    except AssertionError:
        # error for condition 2
except AssertionError:
    # error for condition 1

Even though I think this last way is not pretty recommendable as in treating exceptions.

I know this might seem primarily opinion-based, but for me it is not since all languages have style guidelines that produce a more sustainable, scalable and readable environment depending on its characteristics and functionalities. I would like to know what if there is a recommended way of treating this matter inside methods and why.