Tutorial Five

Tutorial Five: More Sogetto Cavato with Conditions

Introduction

In Tutorial Four, we created a function that would return solfege from the vowels in a string.

In this Tutorial, we'll add some conditions to our function. These conditions will help to accomodate other possibilities and situations that might come up. Even though it's more code, it's code that can produce more interesting results, as well as deal with situations we couldn't anticipate in the previous tutorial.

What Conditions Exist?

In our previous example, we could only deal with the sogetto cavato directly used in Josquin's Vive le roi. In effect, the code written only deals with four conditions, mapped to the four notes in the cantus firmus. Those letters are 'v,' 'e,' 'i,' and 'o.' Even though we can render a Vive le roi, there's plenty of letters left in the alphabet we haven't dealt with, not to mention non-letter parts of strings like spaces and periods.

For now, let's keep things simple, and focus just on the possibilities for solfège. If we keep the "ut" for "do," and ignore "ti" (as Josquin didn't have a "ti" to work with), we'd have these possible vowels (plus 'v'):

solefge_list = ['a', 'e', 'i', 'o', 'u', 'v']

The fact that these map to our vowels isn't an accident. But wait! If we go through solfège, we have "do, re, mi, fa, sol, la" - two 'a' situations!

We can totally address this in the code. The good news is that Python dictionaries don't let you have two identical key values. This is great for solving the problem, but we still have two possible interpretations of translating 'a' to a note.

This is where using conditions can help. We can create a "fa" and a "la" in our list, and use some programming to accomodate having both these conditions.

And, as we move on to dealing with these conditions, we should note we already used a condition in the previous tutorial! This line of code:

    if letter in solfege_vowels:

Evaluates if the letter is one we can deal with. Let's make this more sophisticated and have more options.

The New Solfège Dictionary

Our new dictionary with all the possibilities would look something like this:

solefge_dict = {
    'u': 0,
    'v': 0,
    'e': 2,
    'i': 4,
    'fa': 5,
    'o': 7,
    'la': 9,
    }

Now, we've dealt with the fact we could have 'fa' or 'la'. There's a problem, though. The previous tutorial code that iterates through the string iterates through each letter individually. It will never return a 5 or 9 because the keys are two letters long. Therefore, our previous tutorial will need adjustments to accomodate our two letter strings fa and la.

Concatenating to Produce 2-letter Strings

Python is nice and has overloaded operators for math symbols. It's fun because we can "add" two strings together to get a longer string. Super fun. So, adding 'l' and 'a' will give us 'la'. This is great, because it's exactly what we need. In action:

l = 'l'
a = 'a'

la = l + a

Indexing to Get Other Locations in an Iteration

Python allows us simply to iterate over any iterable data type. This is nice, but sometimes we need an index to solve some problems. To allow this, Python has an enumerate function that will allow access to the indices.

To use enumerate we simply add it to a loop, like so:

vlr = 'viveleroi'

for idx, letter in enumerate(vlr):
    print(idx, letter)

This will print this:

0, 'v'
1, 'i'
2, 'v'
3, 'e'
4, 'l'
5, 'e'
6, 'r'
7, 'o'
8, 'i'

Combining enumerate and Concatenation

If we combine both of the last bits of code, we can create a function that will iterate over a string, and return a plus whatever letter comes before it.

from py2musicxml.notation import Note, Part, Score

vlr = 'viveleroi'

solefge_dict = {
    'u': 0,
    'v': 0,
    'e': 2,
    'i': 4,
    'fa': 5,
    'o': 7,
    'la': 9,
    }

solfege_vowels = []

for key, value in sc_dict:
    solfege_vowels.append(key)

def modified_get_cantus_firmus(string_to_convert):
    note_list = []
    for idx, letter in enumerate(string_to_convert):
        if letter == 'a' and idx != 0:
            concat_letter = string_to_convert[idx - 1] + letter
            note_list.append(solefge_dict[concat_letter])
        elif letter in solfege_vowels:
            note_list.append(solefge_dict[letter])
        else:
            pass

vlr_note_list = modified_get_cantus_firmus(vlr)

time_sig = [(2,2)]

vlr_part = Part([vlr_note_list], time_sig)

vlr_score = Score([vlr_part])

vlr_score.convert_to_xml("vlr_cantus_firmus.musicxml")

The result will be the same as our previous tutorial:

Of course, the Vive le roi letters don't use our new code! Let's try some letters that will invoke our code.

from py2musicxml.notation import Note, Part, Score

vlr = 'landolakes'

solefge_dict = {
    'u': 0,
    'v': 0,
    'e': 2,
    'i': 4,
    'fa': 5,
    'o': 7,
    'la': 9,
    }

solfege_vowels = []

for key, value in sc_dict:
    solfege_vowels.append(key)

def modified_get_cantus_firmus(string_to_convert):
    note_list = []
    for idx, letter in enumerate(string_to_convert):
        if letter == 'a' and idx != 0:
            concat_letter = string_to_convert[idx - 1] + letter
            note_list.append(solefge_dict[concat_letter])
        elif letter in solfege_vowels:
            note_list.append(solefge_dict[letter])
        else:
            pass

vlr_note_list = modified_get_cantus_firmus(vlr)

time_sig = [(2,2)]

vlr_part = Part([vlr_note_list], time_sig)

vlr_score = Score([vlr_part])

vlr_score.convert_to_xml("vlr_cantus_firmus.musicxml")

We can, just like Josquin, write a mass based on a text. In our case, we're using delicious cream and dairy products. But, if we run this code, we'll get this as a result:

I'll leave it as a task for the reader to decide how to deal with an 'a' without and 'f' or 'l' before it, and how to write that code. So many possibilities!