def format_compound_unit(
    numerator_value, numerator_unit=None,
    denominator_value=1, denominator_unit=None,
    length='long', format=None, locale=LC_NUMERIC
):
    locale = Locale.parse(locale)

    # Look for a specific compound unit first...

    if numerator_unit and denominator_unit and denominator_value == 1:
        compound_unit = _find_compound_unit(numerator_unit, denominator_unit, locale=locale)
        if compound_unit:
            return format_unit(numerator_value, compound_unit, length=length, format=format, locale=locale)

    # ... failing that, construct one "by hand".

    if isinstance(numerator_value, string_types):  # Numerator is preformatted
        formatted_numerator = numerator_value
    elif numerator_unit:  # Numerator has unit
        formatted_numerator = format_unit(
            numerator_value, numerator_unit, length=length, format=format, locale=locale
        )
    else:  # Unitless numerator
        formatted_numerator = format_decimal(numerator_value, format=format, locale=locale)

    if isinstance(denominator_value, string_types):  # Denominator is preformatted
        formatted_denominator = denominator_value
    elif denominator_unit:  # Denominator has unit
        if denominator_value == 1:  # support perUnitPatterns when the denominator is 1
            denominator_unit = _find_unit_pattern(denominator_unit, locale=locale)
            per_pattern = locale._data["unit_patterns"].get(denominator_unit, {}).get(length, {}).get("per")
            if per_pattern:
                return per_pattern.format(formatted_numerator)
            # See TR-35's per-unit pattern algorithm, point 3.2.
            # For denominator 1, we replace the value to be formatted with the empty string;
            # this will make `format_unit` return " second" instead of "1 second".
            denominator_value = ""

        formatted_denominator = format_unit(
            denominator_value, denominator_unit, length=length, format=format, locale=locale
        ).strip()
    else:  # Bare denominator
        formatted_denominator = format_decimal(denominator_value, format=format, locale=locale)

    per_pattern = locale._data["compound_unit_patterns"].get("per", {}).get(length, "{0}/{1}")

    return per_pattern.format(formatted_numerator, formatted_denominator)
Format a compound number value, i.e. "kilometers per hour" or similar.
dataset/ETHPy150Open python-babel/babel/babel/units.py/format_compound_unit