Lecture_3

In this lecture we went over conditional statements, that is, use if statements, and iteration (loops).

A key concept is Boolean contexts. For example:

>>> 4 < 2
False
>>> 5 >= 5
True

And we shall memorize Boolean operators:
>>> True and False
False
>>> True or False
True
>>> not False
True

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A loop example:

def fib(n):
    """Compute the nth Fibonacci number, for n >= 2. """
    pred, curr = 0, 1
    k = 2
    while k < n:
        pred, curr = curr, pred + curr
        k = k + 1
    return curr
result = fib(8)

################

Programmers use assert statements to verify expectations, such as the output of a function being tested. An assert statement has an expression in a boolean context, followed by a quoted line of text that will be displayed if the expression evaluates to a false value.

For example:
assert fib(8) == 13, 'The 8th Fibonacci number should be 13'

When the expression being asserted evaluates to a true value, executing an assert statement has no effect. When it is a false value, assert causes an error that halts execution.When it is a false value, assert causes an error that halts execution. When writing Python in files, rather than directly into the interpreter, tests are typically written in the same file or a neighboring file with the suffix _test.py. That is, you won't see the assert's result in interpreter.

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A new method taught in this lecture is Doctests. The first line of a docstring should contain a one-line description of the function, followed by a blank line. A detailed description of arguments and behavior may follow.
For example:
def sum_naturals(n):
        """Return the sum of the first n natural numbers.

        >>> sum_naturals(10)
        55
        >>> sum_naturals(100)
        5050
        """
        total, k = 0, 1
        while k <= n:
            total, k = total + k, k + 1
        return total
        
we can verify this interaction via the doctest module:

from doctest import testmod # confusing with this command, because nothing happened.
testmod()

we can also use this command:

from doctest import run_docstring_examples
run_docstring_examples(sum_naturals, globals(), True)

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Lecture 3 concluded.

To be honest, I didn't get the last part of this lecture. I don't see the point of running such test. Probably I will find them useful in future, hopefully.