# Source code for en_us_normalization.production.verbalize.fraction

```"""

Verbalizes fractions
"""

import pynini
from en_us_normalization.production.verbalize.cardinal import CardinalFst
from en_us_normalization.production.verbalize.ordinal import OrdinalFst
from pynini.lib import pynutil

from learn_to_normalize.grammar_utils.base_fst import BaseFst
from learn_to_normalize.grammar_utils.shortcuts import SIGMA, insert_space

[docs]class FractionFst(BaseFst):
"""
Finite state transducer for verbalizing fraction.
Fraction consists of integer part, numerator and denominator.
To expand integer part and numerator - cardinal transducer is reused.
For denominator of the fraction however - ordinal transducer is needed.

There are few exception, when fraction (both numerator and denominator) is
expanded as one word (for ex. 1/2 -> half)

Also some denominators (2, 3, 4) require custom expansion (halves, thirds, quarters).

When either numerator or denominator are "1" - this is also a special cases
that has to be handled explicitly.

Examples of input/output strings:

- fraction|integer_part:23|numerator:4|denominator:5| -> twenty three and four fifths

"""

[docs]    def __init__(self, cardinal: CardinalFst = None, ordinal: OrdinalFst = None):
super().__init__(name="fraction")
if cardinal is None:
cardinal = CardinalFst()
if ordinal is None:
ordinal = OrdinalFst(cardinal=cardinal)

# custom denominators are 1, 2, 3 and 4.
# they are expanded differently then the rest.
custom_denominator = (
pynini.cross("1", "over one")
| pynini.cross("2", "halves")
| pynini.cross("3", "thirds")
| pynini.cross("4", "quarters")
)
custom_denominator = (
pynutil.delete("denominator:") + custom_denominator + pynutil.delete("|")
)

# standard denominators expanded with ordinal transducer
standard_denominator = (
pynutil.delete("denominator:")
+ ordinal.get_ordinal_expanding_fst()
+ pynutil.delete("|")
)

# numerators are expanded with cardinal transducer
standard_numerator = (
pynutil.delete("numerator:")
+ cardinal.get_cardinal_expanding_fst()
+ pynutil.delete("|")
)
# custom numerator where value is "1".
one_numerator = pynini.cross("numerator:1|", "one")

# when numerator is "1", denominator is singular.
# only standard denominator is handled because customs are within single word fraction
singular_fraction = one_numerator + insert_space + standard_denominator
# when numerator >1, standard denominator is plural, but custom one is not
standard_denominator + pynutil.insert("s"), 1.1
)
plural_fraction = standard_numerator + insert_space + denominator
# custom fractions that are expanded as single word: 1/2, 1/3, 1/4
single_word_fraction = (
pynini.cross("2", "half")
| pynini.cross("3", "third")
| pynini.cross("4", "quarter")
)
single_word_fraction = (
pynini.cross("numerator:1|denominator:", "a ")
+ single_word_fraction
+ pynutil.delete("|")
)
fraction = (
single_word_fraction
)

# expanding integer part as cardinal
integer = (
pynutil.delete("integer_part:")
+ cardinal.get_cardinal_expanding_fst()
+ pynutil.delete("|")
)
# fraction doesn't always have integer part
optional_integer = pynini.closure(integer + pynutil.insert(" and "), 0, 1)

optional_sign = pynini.closure(pynini.cross("negative:1|", "minus "), 0, 1)
graph = optional_sign + optional_integer + fraction
# when it's a single word fraction and there is no integer part,
# prefix should be rewritten, i.e.
# it is "1 1/2 -> one and a half"
# but it is "1/2 -> one half"
only_fraction_prefix = pynini.cdrewrite(
pynini.cross("a ", "one "), "[BOS]", "", SIGMA
).optimize()
self.graph = graph @ only_fraction_prefix
self._single_fst = self.delete_tokens(self.graph).optimize()

[docs]    def get_graph(self):
"""
helper function that returns the whole fraction verbalization graph
without token name deletion. this is needed if the whole fraction
graph is reused in another semiotic class (for ex. measure)
"""
return self.graph
```