Functions¶

Here are function descriptions, from simple to more complex, to be used in practicing TDD.

is_zero

Input: the value to be investigated
Returns True if the input is zero
Returns False if the input is not zero
If the input is not one number, a TypeError is raised.

is_zero example implementation

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def is_zero(x):
    """Determine if `x` is zero.

    If `x` is not a number, a `TypeError` is raised.

    Returns `True` if `x` is zero
    """
    if not isinstance(x, (int, float)):
        msg = "'number' must be a number. "
        raise TypeError(
            msg,
            "Actual type of 'number': ", type(x),
        )
    return x == 0

is_even

Input: the value to be investigated
Returns True if the input is even
Returns False if the input is not even
If the input is not one integer, a TypeError is raised.

is_even example implementation

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def is_even(x):
    """Determine if `x` is even.

    If `x` is not an integer number, a `TypeError` is raised.

    Returns `True` if `x` is even
    """
    if not isinstance(x, int):
        msg = "'number' must be a number. Actual type of 'number': "
        raise TypeError(
            msg, type(x),
        )
    return x % 2 == 0

is_odd

Input: the value to be investigated
Returns True if the input is odd
Returns False if the input is not odd
If the input is not one integer, a TypeError is raised.

is_odd example implementation

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def is_odd(x):
    """Determine if `x` is odd.

    If `x` is not an integer number, a `TypeError` is raised.

    Returns `True` if `x` is odd
    """
    return not is_even(x)

If the function is_even is absent, here is a stand-alone implementation:

def is_odd(x):
    """Determine if `x` is odd.

    If `x` is not an integer number, a `TypeError` is raised.

    Returns `True` if `x` is odd
    """
    if not isinstance(x, int):
        msg = "'number' must be a number. Actual type of 'number': "
        raise TypeError(
            msg, type(x),
        )
    return not x % 2 == 0

is_probability(p)

Input: the value to be investigated
Returns True if the input is in the range [0.0, 1.0], that is from and including zero to and including one
Returns False if the input is not in that range
If the input is not one floating point number, a TypeError is raised.

is_probability example implementation

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def is_probability(x):
    """Determine if `x` is a probability.

    Determine if `x` is a probability,
    i.e. a value between 0.0 and 1.0, including both 0.0 and 1.0.
    If `x` is not a floating point number, a `TypeError` is raised.

    Returns `True` if `x` is a probability
    """
    if not isinstance(x, float):
        msg = "'number' must be a floating point number. "
        raise TypeError(
            msg,
            "Actual type of 'number': ", type(x),
        )
    min_probability = 0.0
    max_probability = 1.0
    return x >= min_probability and x <= max_probability

is_number

Input: the value to be investigated
Returns True if the input is a number
Returns False if the input is not a number
If the input is not one element, a TypeError is raised.

is_number example implementation

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def is_number(x):
    """Determine if `x` is one number.

    Determine if `x` is one number,
    for example, '42' or '3.14.

    Returns `True` if `x` is one number
    """
    return isinstance(x, (int, float) )

are_numbers(x)

Input: one value (e.g. a list) to be investigated
Returns True if the input is a list of numbers number
Returns False if the input is not a list of numbers
If the input is an empty list, a TypeError is raised.

are_numbers example implementation

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def are_numbers(x):
    """Determine if `x` is one or more numbers.

    Numbers can be integer or floating point.

    Returns `True` if `x` is one or more numbers.
    """
    if not isinstance(x, list):
        return False
    if len(x) == 0:
        return False
    return all(is_number(e) for e in x)

get_digits

Input: one number to be split in digits
Returns the number split into a list of digits, e.g. 314 become [3, 1, 4]
If the input is not one integer, or is negative, a TypeError is raised.

get_digits example implementation

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def get_digits(x):
    """Get the digits of an integer number.

    Get the digits of an integer number,
    for example, '123' becomes '[1, 2, 3]'
    and '0' becomes '[0]'.
    Negative numbers have only their digits collected,
    for example, '-123' becomes '[1, 2, 3]'.

    Will raise TypeError if `x` is not an integer.
    """
    if not isinstance(x, int):
        message = "'x' must be an integer"
        raise TypeError(message)
    zero = 0
    if x < zero:
        return get_digits(-x)
    digits = []
    digits_in_numbering_system = 10
    while True:
        digits.insert(0, x % digits_in_numbering_system)
        if x < digits_in_numbering_system:
            return digits
        x = x // digits_in_numbering_system

get_digits example implementation in a video?

YouTube video showing how to develop get_digits using TDD

is_roman_numeral

Input: one string to be checked if it is a roman numeral
Returns True if the input is a roman numeral, e.g. 'I', 'II', 'IV', 'XI', etc.
Returns False if the input is not a roman numeral
If the input is not one String, a TypeError is raised.

sum_divisors(x)

Returns the sum of the proper divisors of the input. For example, the proper divisors of 4 are 1 and 2, as 4 can be divided by both 1 and 2.

Input	Expected output
1	0
2	1
3	1
4	1+2=3
5	1
6	1+2+3=6
7	1
8	1+2+4=7

If the input is not one integer that is at least one, a TypeError is raised.

is_prime

Function name: is_prime
Output:
- Returns True if the input is a prime number.
- Returns False if the input is not a prime number.
- Gives an error when the input is not one number

int_to_roman(x)

Input: an integer
Returns The a Roman numeral of the same value as a string, e.g. 'IV'

Input	Expected output
0	[an empty string]
1	I
2	II
3	III
4	IV
5	V
6	VI
7	IX

If the input is not one integer that is at least zero, a TypeError is raised.

roman_to_int(x)

Input: a Roman numeral, e.g. IV
Returns: the integer value of this Roman numeral

Input	Expected output
I	1
II	2
III	3
IV	4
V	5
VI	6
IX	9

If the input is not one valid roman numeral, a TypeError is raised.

Too easy? Try Project Euler

Go ahead and write a function to solve a question at Project Euler.

Other example implementations¶

are_strings

Function name: are_strings
Output:
- Returns True if the input is one or more strings.
- Returns False otherwise.

are_strings example implementation

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def are_strings(x):
    """Determine if `x` is one or more strings.

    Returns `True` if `x` is one or more strings.
    """
    if not isinstance(x, list):
        return False
    if len(x) == 0:
        return False
    return all(is_string(e) for e in x)

check_are_strings

Function name: check_are_strings
Input: the value to be checked
Output:
- Returns nothing
- Raises an exception when the input is not one or more strings

check_are_strings example implementation

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def check_are_strings(x):
    """Determine if `x` is one or more strings.

    If `x` is not one or more strings, a `RuntimeError` is raised.

    Returns nothing.
    """
    if not are_strings(x):
        msg = "'x' must be strings. "
        raise RuntimeError(
            msg,
            "Actual value of 'x': ", x,
        )

check_different

Function name: check_different
Input: the two values to be compared
Output:
- Returns nothing
- Raises an exception when the two input values are different

check_different example implementation

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def check_different(a, b):
    """Determine if `a` and `b` are different.

    Raises `RuntimeError` when not.

    Returns nothing.
    """
    if a == b:
        msg = "'a' and 'b' must be different. "
        raise RuntimeError(
            msg,
            "Value of 'a': ", a,
        )

check_equal example implementation

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def check_equal(a, b):
    """Determine if `a` and `b` are equal.

    Raises `RuntimeError` when not.

    Returns nothing.
    """
    if a != b:
        msg = "'a' and 'b' must be equal. "
        raise RuntimeError(
            msg,
            "Value of 'a': ", a, ". ",
            "Value of 'b': ", b,
        )

check_is_number example implementation

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def check_is_number(x):
    """Determine if `x` is a number.

    If `x` is not a number, a `RuntimeError` is raised.

    Returns nothing.
    """
    if not is_number(x):
        msg = "'x' must be a number. "
        raise RuntimeError(
            msg,
            "Actual value of 'x': ", x,
        )

check_is_probability example implementation

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def check_is_probability(x):
    """Determine if `x` is a probability.

    If `x` is not a probability, a `RuntimeError` is raised.

    Returns nothing.
    """
    check_is_number(x)
    if not is_probability(x):
        msg = "'x' must be a probability. "
        raise RuntimeError(
            msg,
            "Actual value of 'x': ", x,
        )

is_string example implementation

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def check_is_string(x):
    """Determine if `x` is a string.

    If `x` is not a string, a `RuntimeError` is raised.

    Returns nothing.
    """
    if not is_string(x):
        msg = "'x' must be a string. "
        raise RuntimeError(
            msg,
            "Actual value of 'x': ", x,
        )

divide_safely example implementation

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def divide_safely(a, b):
    """Divide `a` by `b`.

    If `a` or `b` are not a floating point number, a `TypeError` is raised.
    If `b` is `0.0`, a `RuntimeError` is raised.

    Returns `a` divided by `b`
    """
    zero = 0.0
    if b == zero:
        msg = "'b' must not be zero"
        raise RuntimeError(
            msg,
        )
    return a / b

is_dividable_by_three example implementation

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def is_dividable_by_three(x):
    """Determine if `x` is dividable by three.

    If `x` is not an integer number, a `TypeError` is raised.

    Returns `True` if `x` is dividable by three
    """
    if not isinstance(x, int):
        msg = "'number' must be a number. Actual type of 'number': "
        raise TypeError(
            msg, type(x),
        )
    return x % 3 == 0

is_string example implementation

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def is_string(x):
    """Determine if `x` is one string.

    Returns `True` if `x` one string
    """
    return isinstance(x, str)

flip_coin example implementation

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from random import randint

def flip_coin():
    """Produce a random boolean."""
    return randint(0, 1) > 0 # noqa: S311

roll_dice example implementation

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from random import randint

def roll_dice():
    """Produce a random integer, similar to a dice toll."""
    return randint(1, 6) # noqa: S311

sum_primes example implementation

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def sum_primes(num):
    """Calculate the sum of all primes up to the given number."""
    if not isinstance(num, int):
        message = "'num' must be an integer"
        raise TypeError(message)
    primes = []
    two = 2
    if num > two:
        primes.append(two)
    elif num == two:
        return(two)
    else:
        return(0)
    for i in range(3, num+1, 2):
        not_prime = False
        for j in range(1, i):
            if i%j == 0 and j != 1:
                not_prime = True
                break
        if not not_prime:
            primes.append(i)
    return sum(primes)