Functions (very basic)

Functions (very basic)#

Education objectives

  • def

  • simple arguments

  • docstring

  • return

A function is a block of organized, reusable code that is used to perform a single, related action. Functions provide better modularity for your application and a high degree of code reusing.

Simple function definitions and calls#

Function blocks begin with the keyword def followed by the function name and parentheses (()).

  • The code block within every function starts with a colon (:) and is indented.

  • Any input parameters or arguments should be placed within these parentheses.

def print_hello():
    "hello printer"
    print("hello")


def myprint(my_var):
    "my hello printer"
    print("I print", my_var)


# function calls
print_hello()
print_hello()
myprint("First call of myprint")
myprint("Second call of myprint")

hello
hello
I print First call of myprint
I print Second call of myprint

  • The first statement of a function can be the documentation string of the function, also called “docstring”.

  • The statement return [expression] exits a function, optionally passing back an expression to the caller. No return statement or a return statement with no arguments is the same as return None.

Duck typing

In computer programming, duck typing is an application of the duck test—“If it walks like a duck and it quacks like a duck, then it must be a duck”—to determine whether an object can be used for a particular purpose

Duck typing on Wikipedia

def add(arg0, arg1):
    """Print and return the sum of the two arguments (duck typing)."""
    result = arg0 + arg1
    print("result = ", result)
    return result

add(2, 3)

result =  5

5

add("a", "b")

result =  ab

'ab'

Exercise 19

Write a function that returns the sum of the first argument with twice the second argument.

def add_second_twice(arg0, arg1):
    """Return the sum of the first argument with twice the second one.
    Arguments should be of type that support sum and product by
    an integer (e.g. numerical, string, list, ...)

    :param arg0: first argument
    :param arg1: second argument
    :return: arg0 + 2 * arg1
    """
    ...

Exercise 20 (Parsing file0.n.txt)

Same exercise as Parsing file0.1.txt but process many files and print file base statistics and overall statistics:

Example of output

python3 step0.2.py
file = "../data/file0.1.txt"
nb = 78   ; sum = 42.46  ; avg = 0.54
file = "../data/file0.2.txt"
nb = 100  ; sum = 53.29  ; avg = 0.53
file = "../data/file0.3.txt"
nb = 25   ; sum = 12.72  ; avg = 0.51
# total over all files:
nb = 203  ; sum = 108.47 ; avg = 0.53

The first step consist in taking the code from the previous parsing exercise and create a function that takes a filename as input and print the statistics:

def compute_stats(file_name):
    """computes the statistics of data in file_name
    :param file_name: the name of the file to process
    :type file_name: str
    :return: the statistics
    :rtype: a tuple (number, sum, average)
    """
    pass

This function can simply be called for each file.

Solution to Exercise 20 (Parsing file0.n.txt)

Show the solution
#!/usr/bin/python3
"""computes basic statistics (size, sum and average) on files
containing lines with one float.
"""


def compute_stats(path):
    """
    computes the statistics of data in a file.
    :param path: the path of the file to process
    :type path: str
    :return: the statistics
    :rtype: a tuple (size, sum, average)
    """
    total_sum = 0.0
    size = 0
    with open(path, encoding="utf-8") as handle:
        for line in handle:
            elem = float(line)
            total_sum += elem
            size += 1

    return (size, total_sum, total_sum / float(size))


file_paths = [f"../file0.{i}.txt" for i in range(1, 4)]

sizes = []
sums = []

for file_path in file_paths:
    (file_size, file_sum, file_avg) = compute_stats(file_path)
    sizes.append(file_size)
    sums.append(file_sum)


for index, file_path in enumerate(file_paths):
    print(
        f"file = {file_path}\n"
        f"size = {sizes[index]:<5}; "
        f" sum = {sums[index]:<7,.2f}; "
        f"avg = {sums[index] / sizes[index]:<5,.2f}"
    )

all_sum = sum(sums)
all_sizes = sum(sizes)
avg = all_sum / all_sizes
print(
    f"# total over all files:\nsize = {all_sizes: <5};"
    f" sum = {all_sum:<7,.2f}; avg = {avg:.2f}"
)
Contents