Development - Advanced, exercise 11

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The function multiple replace allows one to replace either all or a fixed number of occurrences of a given character in a list with another character contained in an input list of characters. In particular, it takes in input four different values: the full string that should be modified, the character to replace in the string, a non-empty list of characters to use as replacement, and the number of occurrences of the character to replace that should be substituted with the related replacement (None means all).

Every time the function finds a character to replace c_i, it substitutes it with the character in the list of replacements positioned in the index equal to the number of occurrences of c that precedes c_i (c₁, c₂, …, c_i-1). In case such number of occurrences that precedes c_i is greater than the maximum index in the list of replacements, the function starts again from the beginning of the list of replacements. For instance:

• multiple_replace("mamma mia!", "m", ["n"], 3) returns "nanna mia!";
• multiple_replace("mamma mia!", "m", ["p", "l", "l"], 3) returns "palla mia!";
• multiple_replace("mamma mia!", "m", ["n", "s", "t"], None) returns "nasta nia!".

Write a function in Python – def multiple_replace(s, c, r, o) – that takes in input the string to modify (s), the character to replace (c), the list of replacements (r), and the maximum number of occurrences of c to replace (o, set to None if one wants to replace all the occurrences), and that returns the modified string.

Solution

# Test case for the function
def test_multiple_replace(s, c, r, o, expected):
    result = multiple_replace(s, c, r, o)
    if expected == result:
        return True
    else:
        return False


# Code of the function
def multiple_replace(s, c, r, o):
    i_o = 0

    if o is None:
        o = len(s)

    for cur_c in s:
        if cur_c == c and i_o < o:
            s = s.replace(c, r[i_o % len(r)], 1)
            i_o += 1

    return s


# Tests
print(test_multiple_replace("mamma mia!", "m", ["n"], 3, "nanna mia!"))
print(test_multiple_replace("mamma mia!", "m", ["p", "l", "l"], 3, "palla mia!"))
print(test_multiple_replace("mamma mia!", "m", ["n", "s", "t"], None, "nasta nia!"))

Additional material

The runnable Python file is available online.