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Progression

progression

Convert chord progressions ↔ roman numeral sequences.

The Progression namespace converts between concrete chord names (in a specific key) and roman-numeral analysis (key-independent).

Example

from tonal_py import Progression

Roman numerals to chords in C major

Progression.from_roman_numerals("C", ["I", "IIm7", "V7"]) ['C', 'Dm7', 'G7']

Chord progression back to roman numerals

Progression.to_roman_numerals("C", ["C", "Dm7", "G7"]) ['I', 'IIm7', 'V7']

Source parity: @tonaljs/progression

from_roman_numerals 

from_roman_numerals(tonic: Any, chords: list[str]) -> list[str]

Convert roman numerals to concrete chord names in a key.

Parameters:

Name Type Description Default
tonic Any

The key's tonic note.

 required
chords list[str]

List of roman-numeral chord strings.

 required

Returns:

Type Description
list[str]

List of concrete chord names.
Example

from tonal_py import Progression Progression.from_roman_numerals("C", ["I", "IIm7", "V7"]) ['C', 'Dm7', 'G7'] Progression.from_roman_numerals("G", ["I", "vi", "IV", "V"]) ['G', 'E', 'C', 'D']

Source code in src/tonal_py/progression.py 
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def from_roman_numerals(tonic: Any, chords: list[str]) -> list[str]:
    """Convert roman numerals to concrete chord names in a key.

    Args:
        tonic: The key's tonic note.
        chords: List of roman-numeral chord strings.

    Returns:
        List of concrete chord names.

    Example:
        >>> from tonal_py import Progression
        >>> Progression.from_roman_numerals("C", ["I", "IIm7", "V7"])
        ['C', 'Dm7', 'G7']
        >>> Progression.from_roman_numerals("G", ["I", "vi", "IV", "V"])
        ['G', 'E', 'C', 'D']
    """
    rns = [roman_numeral.get(c) for c in chords]
    return [
        _pitch_distance.transpose(tonic, _pitch_interval.interval(rn).name) + rn.chord_type
        for rn in rns
    ]

to_roman_numerals 

to_roman_numerals(tonic: Any, chords: list[str]) -> list[str]

Convert concrete chord names to roman numerals relative to a key.

Parameters:

Name Type Description Default
tonic Any

The key's tonic note.

 required
chords list[str]

List of chord names.

 required

Returns:

Type Description
list[str]

List of roman-numeral analysis strings.
Example

from tonal_py import Progression Progression.to_roman_numerals("C", ["C", "Dm7", "G7"]) ['I', 'IIm7', 'V7']

Source code in src/tonal_py/progression.py 
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def to_roman_numerals(tonic: Any, chords: list[str]) -> list[str]:
    """Convert concrete chord names to roman numerals relative to a key.

    Args:
        tonic: The key's tonic note.
        chords: List of chord names.

    Returns:
        List of roman-numeral analysis strings.

    Example:
        >>> from tonal_py import Progression
        >>> Progression.to_roman_numerals("C", ["C", "Dm7", "G7"])
        ['I', 'IIm7', 'V7']
    """
    out: list[str] = []
    for chord in chords:
        note, chord_type, _bass = _chord_mod.tokenize(chord)
        interval_name = _pitch_distance.distance(tonic, note)
        roman = roman_numeral.get(_pitch_interval.interval(interval_name))
        out.append(roman.name + chord_type)
    return out