Impression of Week 4

    The forth week, we did recursion. It is a function but it's using itself in the function. Recursions are used to solve questions that requires unknown loops to check the nested-list inside the nested-list. For example:
 def rec_max(L):

    ''' (list or int) -> int

    Return L if it's an int, or the maximum int in L,
    a possibly nested list of numbers.

    Assume: L is an int or non-empty list

    >>> rec_max([17, 21, 0])
    21
    >>> rec_max([17, [21, 24], 0])
    24
    '''
    if isinstance(L, list):
        return max([rec_max(x) for x in L])
    else:
        return L

In this function, the function re_max is called again and again until we find the elements that are not lists and the loop stops.
We did a lot of tracing in the lecture and in the tutorial, starting with depth 0 and moved on to more complicated examples gradually. We can also find the docstring by calling and tracing examples, just like we did in the tutorial.
By calling non-lists or empty list, we get the special cases of the function. How I understand this is checking the 'else:' and checking the build-in method called in the recursion. Then we check examples with more depth, and we can conclude the docstring and the assumption.

The first term test is next week, wish everyone a good grade!