Docstrings, preconditions, and postconditions A docstring is a triple-quoted string that appears right after a function header. Its audience is another program, or maybe you, a few months after you wrote the function. It is a brief reference describing what the function does.

A good way to manage this is to have two sections.

Preconditions These describe anything that shhould be true before the function is called. This can include a description of the number and types of inputs the function should have.

Postconditions These describe anything that should be true after the function is called. Here, describe any return value and any side-effects calling the function produces.

My function assignments will be speced in this way.

Whats up __doc__? The standard functions all have docstrings. Here we see some examples.

>>> print(len.__doc__)
Return the number of items in a container.
>>> print(ord.__doc__)
Return the Unicode code point for a one-character string.
>>> print(bin.__doc__)
Return the binary representation of an integer.

   >>> bin(2796202)
   '0b1010101010101010101010'
>>> print(print.__doc__)
print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)

Prints the values to a stream, or to sys.stdout by default.
Optional keyword arguments:
file:  a file-like object (stream); defaults to the current sys.stdout.
sep:   string inserted between values, default a space.
end:   string appended after the last value, default a newline.
flush: whether to forcibly flush the stream.

You can also get information a function by calling the help function on it in an interactive session.

Simple if An if requires a predicate, which is a boolean-valued expression. If the predicate evaluates to True, the CODE executes. Otherwise CODE gets skipped.

if predicate:
    CODE

This absolute value function has a simple if in it.

def f(x):
    if x < 0:   #simple if
        x = -x
    return x

def pass_NJ_license(score):
    if score >= 80:
        return "PASS"
    else:
        return "FAIL"

x = input("Enter a score:  ")
x = int(x)
print(f"Your result is {pass_NJ_license(x)}")

Fork it: if/else The if-else progression looks like this. If the predicate evaluates to True the block TRUE_CODE executes. Otherwise, the block FALSE_CODE executes. Something is guaranteed to happen. This is a two-tined fork.

if predicate:
    TRUE_CODE
else:
    FALSE_CODE

if predicate1:
    CODE_1
elif predicate2:
    CODE_2

    .
    .
    .


elif predicateN:
    CODE_N
else:
    CODE_DEFAULT