Exercises day 1

We will work on these exercises during the course. Do not worry about them before the course.

Below you find the source code for the exercises. Copy and paste them into a file called e.g. basics.py. It is OK to copy all or just one or two exercises to start with. We give you the tests and you need to code the functions to make the tests pass. It is OK to work in pairs and it is OK to use Google and Stack Overflow.

You can run the tests like this:

$ py.test -s -vv basics.py

You can also run a single test, e.g.:

$ py.test -s -vv -k test_reverse_list basics.py

Basics

Make the following tests green:

def reverse_list(l):
    """
    Reverses order of elements in list l.
    """
    return None


def test_reverse_list():
    assert reverse_list([1, 2, 3, 4, 5]) == [5, 4, 3, 2, 1]


# ------------------------------------------------------------------------------

def reverse_string(s):
    """
    Reverses order of characters in string s.
    """
    return None


def test_reverse_string():
    assert reverse_string("foobar") == "raboof"


# ------------------------------------------------------------------------------

def get_word_lengths(s):
    """
    Returns a list of integers representing
    the word lengths in string s.
    """
    return None


def test_get_word_lengths():
    text = "Three tomatoes are walking down the street"
    assert get_word_lengths(text) == [5, 8, 3, 7, 4, 3, 6]


# ------------------------------------------------------------------------------

def find_longest_word(s):
    """
    Returns the longest word in string s.
    In case there are several, return the first.
    """
    return None


def test_find_longest_word():
    text = "Three tomatoes are walking down the street"
    assert find_longest_word(text) == "tomatoes"
    text = "foo foo1 foo2 foo3"
    assert find_longest_word(text) == "foo1"


# ------------------------------------------------------------------------------

def remove_substring(substring, string):
    """
    Returns string with all occurrences of substring removed.
    """
    return None


def test_remove_substring():
    assert remove_substring("don't", "I don't like cake") == "I  like cake"
    assert remove_substring("bada", "bada-bing-bada-bing") == "-bing--bing"


# ------------------------------------------------------------------------------

def read_column(file_name, column_number):
    """
    Reads column column_number from file file_name
    and returns the values as floats in a list.
    """
    return None


def test_read_column():

    import tempfile
    import os

    text = """1   0.1  0.001
2   0.2  0.002
3   0.3  0.003
4   0.4  0.004
5   0.5  0.005
6   0.6  0.006"""

    # we save this text to a temporary file
    file_name = tempfile.mkstemp()[1]
    with open(file_name, 'w') as f:
        f.write(text)

    # and now we pass the file name to the function which will read the column
    assert read_column(file_name, 2) == [0.1, 0.2, 0.3, 0.4, 0.5, 0.6]

    # we remove the temporary file
    os.unlink(file_name)


# ------------------------------------------------------------------------------

def histogram(l):
    """
    Converts a list of tuples into a simple string histogram.
    """
    return None


def test_histogram():
    assert histogram([('a', 2), ('b', 5), ('c', 1)]) == """a: ##
b: #####
c: #"""


# ------------------------------------------------------------------------------

def character_statistics(text):
    """
    Reads text from file file_name, then
    lowercases the text, and then returns
    a list of tuples (character, occurence)
    sorted by occurence with most frequent
    appearing first.
    Use the isalpha() method to figure out
    whether the character is in the alphabet.
    """
    return None


def test_character_statistics():

    text = """
To be, or not to be: that is the question:
Whether 'tis nobler in the mind to suffer
The slings and arrows of outrageous fortune,
Or to take arms against a sea of troubles,
And by opposing end them? To die: to sleep;
No more; and by a sleep to say we end
The heart-ache and the thousand natural shocks
That flesh is heir to, 'tis a consummation
Devoutly to be wish'd. To die, to sleep;
To sleep: perchance to dream: ay, there's the rub;
For in that sleep of death what dreams may come
When we have shuffled off this mortal coil,
Must give us pause: there's the respect
That makes calamity of so long life;
For who would bear the whips and scorns of time,
The oppressor's wrong, the proud man's contumely,
The pangs of despised love, the law's delay,
The insolence of office and the spurns
That patient merit of the unworthy takes,
When he himself might his quietus make
With a bare bodkin? who would fardels bear,
To grunt and sweat under a weary life,
But that the dread of something after death,
The undiscover'd country from whose bourn
No traveller returns, puzzzles the will
And makes us rather bear those ills we have
Than fly to others that we know not of?
Thus conscience does make cowards of us all;
And thus the native hue of resolution
Is sicklied o'er with the pale cast of thought,
And enterprises of great pith and moment
With this regard their currents turn awry,
And lose the name of action.--Soft you now!
The fair Ophelia! Nymph, in thy orisons
Be all my sins remember'd."""

    assert character_statistics(text) == [('e', 146), ('t', 120), ('o', 99), ('s', 88), ('a', 87),
                                          ('h', 79), ('r', 71), ('n', 70), ('i', 57), ('l', 44),
                                          ('d', 43), ('u', 41), ('f', 36), ('m', 32), ('w', 29),
                                          ('p', 24), ('c', 23), ('y', 18), ('b', 17), ('g', 14),
                                          ('k', 10), ('v', 8), ('z', 3), ('q', 2)]


# ------------------------------------------------------------------------------

def simple_zip(l1, l2):
    """
    Implement a simple zip function.
    Do not use the built-in zip().
    """
    return None


def test_simple_zip():

    assert simple_zip(['a', 'b', 'c'], [1, 2, 3]) == [('a', 1), ('b', 2), ('c', 3)]


# ------------------------------------------------------------------------------

def password_good(password):
    """
    Implement a function that tests if the input string is a "good" password.

    A "good" password should:

    - Be at least 8 characters long
    - Contain at least one upper-case letter [A-Z]
    - Contain at least one lower-case letter [a-z]
    - Contain at least one digit [0-9]
    - Contain at least one special character [#%&]

    The function should return True if the password is good, False otherwise.
    """
    return None


def test_password_good():

    good_passwords = ['Aa0#abcd', 'Zz9&0000', 'ABrt#&%aabb00']

    for pw in good_passwords:
        assert password_good(pw)

    bad_passwords = ['Aa0#', 'Zz9&000', 'ABrtaabb00', 'rt#&%aabb00',
                     'AB#&%001', 'ABrt#&%aabb']

    for pw in bad_passwords:
        assert not password_good(pw)


# ------------------------------------------------------------------------------

def generate_password():
    """
    Write a function that generates a random "good" password. The generated
    password should return True if checked by password_good.

    For easy to remember strong passwords see: https://xkcd.com/936/
    """
    return None


def test_generate_password():

    # generate list of 10 random passwords
    pw_list = []
    for _ in range(10):
        pw_list.append(generate_password())

    # passwords should be random, test for duplicates
    assert len(pw_list) == len(set(pw_list))

    # test all passwords in list
    for pw in pw_list:
        assert password_good(pw)