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==========
inflect.py
==========


NAME
====
inflect.py - Correctly generate plurals, singular nouns, ordinals, indefinite articles; convert numbers to words.

VERSION
=======

This document describes version 0.2.3 of inflect.py

INSTALLATION
============

``pip install inflect``

or

``easy_install inflect``

SYNOPSIS
========

::

 import inflect
 p = inflect.engine()

 # METHODS:

 # plural plural_noun plural_verb plural_adj singular_noun no num
 # compare compare_nouns compare_nouns compare_adjs
 # a an
 # present_participle
 # ordinal number_to_words
 # join
 # inflect classical gender
 # defnoun defverb defadj defa defan


 # UNCONDITIONALLY FORM THE PLURAL

      print "The plural of ", word, " is ", p.plural(word)


 # CONDITIONALLY FORM THE PLURAL

      print "I saw", cat_count, p.plural("cat",cat_count)


 # FORM PLURALS FOR SPECIFIC PARTS OF SPEECH

      print p.plural_noun("I",N1), p.plural_verb("saw",N1), p.plural_adj("my",N2), \
            p.plural_noun("saw",N2)


 # FORM THE SINGULAR OF PLURAL NOUNS

      print "The singular of ", word, " is ", p.singular_noun(word)

 # SELECT THE GENDER OF SINGULAR PRONOUNS

      print p.singular_noun('they')  # 'it'
      p.gender('f')
      print p.singular_noun('they')  # 'she'


 # DEAL WITH "0/1/N" -> "no/1/N" TRANSLATION:

      print "There ", p.plural_verb("was",errors), p.no(" error",errors)


 # USE DEFAULT COUNTS:

      print p.num(N1,""), p.plural("I"), p.plural_verb(" saw"), p.num(N2), p.plural_noun(" saw")
      print "There ", p.num(errors,''), p.plural_verb("was"), p.no(" error")


 # COMPARE TWO WORDS "NUMBER-INSENSITIVELY":

      print "same\n"      if p.compare(word1, word2)
      print "same noun\n" if p.compare_nouns(word1, word2)
      print "same verb\n" if p.compare_verbs(word1, word2)
      print "same adj.\n" if p.compare_adjs(word1, word2)


 # ADD CORRECT "a" OR "an" FOR A GIVEN WORD:

      print "Did you want ", p.a(thing), " or ", p.an(idea)


 # CONVERT NUMERALS INTO ORDINALS (i.e. 1->1st, 2->2nd, 3->3rd, etc.)

      print "It was", p.ordinal(position), " from the left\n"

 # CONVERT NUMERALS TO WORDS (i.e. 1->"one", 101->"one hundred and one", etc.)
 # RETURNS A SINGLE STRING...

    words = p.number_to_words(1234)      # "one thousand, two hundred and thirty-four"
    words = p.number_to_words(p.ordinal(1234)) # "one thousand, two hundred and thirty-fourth"


 # GET BACK A LIST OF STRINGS, ONE FOR EACH "CHUNK"...

    words = p.number_to_words(1234, getlist=True)    # ("one thousand","two hundred and thirty-four")


 # OPTIONAL PARAMETERS CHANGE TRANSLATION:

    words = p.number_to_words(12345, group=1)
    # "one, two, three, four, five"

    words = p.number_to_words(12345, group=2)
    # "twelve, thirty-four, five"

    words = p.number_to_words(12345, group=3)
    # "one twenty-three, forty-five"

    words = p.number_to_words(1234, andword='')
    # "one thousand, two hundred thirty-four"

    words = p.number_to_words(1234, andword=', plus')
    # "one thousand, two hundred, plus thirty-four" #TODO: I get no comma before plus: check perl

    words = p.number_to_words(555_1202, group=1, zero='oh')
    # "five, five, five, one, two, oh, two"

    words = p.number_to_words(555_1202, group=1, one='unity')
    # "five, five, five, unity, two, oh, two"

    words = p.number_to_words(123.456, group=1, decimal='mark')
    # "one two three mark four five six"  #TODO: DOCBUG: perl gives commas here as do I

 # LITERAL STYLE ONLY NAMES NUMBERS LESS THAN A CERTAIN THRESHOLD...

    words = p.number_to_words(   9, threshold=10);    # "nine"
    words = p.number_to_words(  10, threshold=10);    # "ten"
    words = p.number_to_words(  11, threshold=10);    # "11"
    words = p.number_to_words(1000, threshold=10);    # "1,000"

 # JOIN WORDS INTO A LIST:

    mylist = join(("apple", "banana", "carrot"))
        # "apple, banana, and carrot"

    mylist = join(("apple", "banana"))
        # "apple and banana"

    mylist = join(("apple", "banana", "carrot"), final_sep="")
        # "apple, banana and carrot"


 # REQUIRE "CLASSICAL" PLURALS (EG: "focus"->"foci", "cherub"->"cherubim")

      p.classical()               # USE ALL CLASSICAL PLURALS

      p.classical(all=True)       # USE ALL CLASSICAL PLURALS
      p.classical(all=False)      # SWITCH OFF CLASSICAL MODE

      p.classical(zero=True)      #  "no error" INSTEAD OF "no errors"
      p.classical(zero=False)     #  "no errors" INSTEAD OF "no error" 

      p.classical(herd=True)      #  "2 buffalo" INSTEAD OF "2 buffalos"
      p.classical(herd=False)     #  "2 buffalos" INSTEAD OF "2 buffalo"

      p.classical(persons=True)   # "2 chairpersons" INSTEAD OF "2 chairpeople"
      p.classical(persons=False)  # "2 chairpeople" INSTEAD OF "2 chairpersons"

      p.classical(ancient=True)   # "2 formulae" INSTEAD OF "2 formulas"
      p.classical(ancient=False)  # "2 formulas" INSTEAD OF "2 formulae"



 # INTERPOLATE "plural()", "plural_noun()", "plural_verb()", "plural_adj()", "singular_noun()",
 # a()", "an()", "num()" AND "ordinal()" WITHIN STRINGS:

      print p.inflect("The plural of {0} is plural({0})".format(word))
      print p.inflect("The singular of {0} is singular_noun({0})".format(word))
      print p.inflect("I saw {0} plural("cat",{0})".format(cat_count))
      print p.inflect("plural(I,{0}) plural_verb(saw,{0}) plural(a,{1}) plural_noun(saw,{1})".format(N1, N2))
      print p.inflect("num({0},)plural(I) plural_verb(saw) num({1},)plural(a) plural_noun(saw)".format(N1, N2))
      print p.inflect("I saw num({0}) plural("cat")\nnum()".format(cat_count))
      print p.inflect("There plural_verb(was,{0}) no(error,{0})".format(errors))
      print p.inflect("There num({0},) plural_verb(was) no(error)".format(errors))
      print p.inflect("Did you want a({0}) or an({1})".format(thing, idea))
      print p.inflect("It was ordinal({0}) from the left".format(position))


 # ADD USER-DEFINED INFLECTIONS (OVERRIDING INBUILT RULES):

      p.defnoun( "VAX", "VAXen" )  # SINGULAR => PLURAL

      p.defverb( "will" , "shall",  # 1ST PERSON SINGULAR => PLURAL
                "will" , "will",   # 2ND PERSON SINGULAR => PLURAL
                "will" , "will")   # 3RD PERSON SINGULAR => PLURAL

      p.defadj(  "hir"  , "their")  # SINGULAR => PLURAL

      p.defa("h")        # "AY HALWAYS SEZ 'HAITCH'!"

      p.defan(   "horrendous.*" )    # "AN HORRENDOUS AFFECTATION"


DESCRIPTION
===========

The methods of the class ``engine`` in module ``inflect.py`` provide plural
inflections, singular noun inflections, "a"/"an" selection for English words,
and manipulation of numbers as words.

Plural forms of all nouns, most verbs, and some adjectives are
provided. Where appropriate, "classical" variants (for example: "brother" ->
"brethren", "dogma" -> "dogmata", etc.) are also provided.

Single forms of nouns are also provided. The gender of singular pronouns
can be chosen (for example "they" -> "it" or "she" or "he" or "they"). 

Pronunciation-based "a"/"an" selection is provided for all English
words, and most initialisms.

It is also possible to inflect numerals (1,2,3) to ordinals (1st, 2nd, 3rd)
and to english words ("one", "two", "three).

In generating these inflections, ``inflect.py`` follows the Oxford
English Dictionary and the guidelines in Fowler's Modern English
Usage, preferring the former where the two disagree.

The module is built around standard British spelling, but is designed
to cope with common American variants as well. Slang, jargon, and
other English dialects are *not* explicitly catered for.

Where two or more inflected forms exist for a single word (typically a
"classical" form and a "modern" form), ``inflect.py`` prefers the
more common form (typically the "modern" one), unless "classical"
processing has been specified
(see `MODERN VS CLASSICAL INFLECTIONS`).

FORMING PLURALS AND SINGULARS
=============================

Inflecting Plurals and Singulars
--------------------------------

All of the ``plural...`` plural inflection methods take the word to be
inflected as their first argument and return the corresponding inflection.
Note that all such methods expect the *singular* form of the word. The
results of passing a plural form are undefined (and unlikely to be correct).
Similarly, the ``si...`` singular inflection method expects the *plural*
form of the word.

The ``plural...`` methods also take an optional second argument,
which indicates the grammatical "number" of the word (or of another word
with which the word being inflected must agree). If the "number" argument is
supplied and is not ``1`` (or ``"one"`` or ``"a"``, or some other adjective that
implies the singular), the plural form of the word is returned. If the
"number" argument *does* indicate singularity, the (uninflected) word
itself is returned. If the number argument is omitted, the plural form
is returned unconditionally.

The ``si...`` method takes a second argument in a similar fashion. If it is
some form of the number ``1``, or is omitted, the singular form is returned.
Otherwise the plural is returned unaltered.


The various methods of ``inflect.engine`` are:



``plural_noun(word, count=None)``

 The method ``plural_noun()`` takes a *singular* English noun or
 pronoun and returns its plural. Pronouns in the nominative ("I" ->
 "we") and accusative ("me" -> "us") cases are handled, as are
 possessive pronouns ("mine" -> "ours").


``plural_verb(word, count=None)``

 The method ``plural_verb()`` takes the *singular* form of a
 conjugated verb (that is, one which is already in the correct "person"
 and "mood") and returns the corresponding plural conjugation.


``plural_adj(word, count=None)``

 The method ``plural_adj()`` takes the *singular* form of
 certain types of adjectives and returns the corresponding plural form.
 Adjectives that are correctly handled include: "numerical" adjectives
 ("a" -> "some"), demonstrative adjectives ("this" -> "these", "that" ->
 "those"), and possessives ("my" -> "our", "cat's" -> "cats'", "child's"
 -> "childrens'", etc.)


``plural(word, count=None)``

 The method ``plural()`` takes a *singular* English noun,
 pronoun, verb, or adjective and returns its plural form. Where a word
 has more than one inflection depending on its part of speech (for
 example, the noun "thought" inflects to "thoughts", the verb "thought"
 to "thought"), the (singular) noun sense is preferred to the (singular)
 verb sense.

 Hence ``plural("knife")`` will return "knives" ("knife" having been treated
 as a singular noun), whereas ``plural("knifes")`` will return "knife"
 ("knifes" having been treated as a 3rd person singular verb).

 The inherent ambiguity of such cases suggests that,
 where the part of speech is known, ``plural_noun``, ``plural_verb``, and
 ``plural_adj`` should be used in preference to ``plural``.


``singular_noun(word, count=None)``

 The method ``singular_noun()`` takes a *plural* English noun or
 pronoun and returns its singular. Pronouns in the nominative ("we" ->
 "I") and accusative ("us" -> "me") cases are handled, as are
 possessive pronouns ("ours" -> "mine"). When third person
 singular pronouns are returned they take the neuter gender by default
 ("they" -> "it"), not ("they"-> "she") nor ("they" -> "he"). This can be
 changed with ``gender()``.

Note that all these methods ignore any whitespace surrounding the
word being inflected, but preserve that whitespace when the result is
returned. For example, ``plural(" cat  ")`` returns " cats  ".


``gender(genderletter)``

 The third person plural pronoun takes the same form for the female, male and
 neuter (e.g. "they"). The singular however, depends upon gender (e.g. "she",
 "he", "it" and "they" -- "they" being the gender neutral form.) By default
 ``singular_noun`` returns the neuter form, however, the gender can be selected with
 the ``gender`` method. Pass the first letter of the gender to
 ``gender`` to return the f(eminine), m(asculine), n(euter) or t(hey)
 form of the singular. e.g.
 gender('f') followed by singular_noun('themselves') returns 'herself'.

Numbered plurals
----------------

The ``plural...`` methods return only the inflected word, not the count that
was used to inflect it. Thus, in order to produce "I saw 3 ducks", it
is necessary to use::

    print "I saw", N, p.plural_noun(animal,N)

Since the usual purpose of producing a plural is to make it agree with
a preceding count, inflect.py provides a method
(``no(word, count)``) which, given a word and a(n optional) count, returns the
count followed by the correctly inflected word. Hence the previous
example can be rewritten::

    print "I saw ", p.no(animal,N)

In addition, if the count is zero (or some other term which implies
zero, such as ``"zero"``, ``"nil"``, etc.) the count is replaced by the
word "no". Hence, if ``N`` had the value zero, the previous example
would print the somewhat more elegant::

    I saw no animals

rather than::

    I saw 0 animals

Note that the name of the method is a pun: the method
returns either a number (a *No.*) or a ``"no"``, in front of the
inflected word.


Reducing the number of counts required
--------------------------------------

In some contexts, the need to supply an explicit count to the various
``plural...`` methods makes for tiresome repetition. For example::

    print plural_adj("This",errors), plural_noun(" error",errors), \
          plural_verb(" was",errors), " fatal."

inflect.py therefore provides a method
(``num(count=None, show=None)``) which may be used to set a persistent "default number"
value. If such a value is set, it is subsequently used whenever an
optional second "number" argument is omitted. The default value thus set 
can subsequently be removed by calling ``num()`` with no arguments.
Hence we could rewrite the previous example::

    p.num(errors)
    print p.plural_adj("This"), p.plural_noun(" error"), p.plural_verb(" was"), "fatal."
    p.num()

Normally, ``num()`` returns its first argument, so that it may also
be "inlined" in contexts like::

    print p.num(errors), p.plural_noun(" error"), p.plural_verb(" was"), " detected."
    if severity > 1:
        print p.plural_adj("This"), p.plural_noun(" error"), p.plural_verb(" was"), "fatal."

However, in certain contexts (see `INTERPOLATING INFLECTIONS IN STRINGS`)
it is preferable that ``num()`` return an empty string. Hence ``num()``
provides an optional second argument. If that argument is supplied (that is, if
it is defined) and evaluates to false, ``num`` returns an empty string
instead of its first argument. For example::

    print p.num(errors,0), p.no("error"), p.plural_verb(" was"), " detected."
    if severity > 1:
        print p.plural_adj("This"), p.plural_noun(" error"), p.plural_verb(" was"), "fatal."
    


Number-insensitive equality
---------------------------

inflect.py also provides a solution to the problem
of comparing words of differing plurality through the methods
``compare(word1, word2)``, ``compare_nouns(word1, word2)``,
``compare_verbs(word1, word2)``, and ``compare_adjs(word1, word2)``.
Each  of these methods takes two strings, and  compares them
using the corresponding plural-inflection method (``plural()``, ``plural_noun()``,
``plural_verb()``, and ``plural_adj()`` respectively).

The comparison returns true if:

- the strings are equal, or
- one string is equal to a plural form of the other, or
- the strings are two different plural forms of the one word.


Hence all of the following return true::

    p.compare("index","index")      # RETURNS "eq"
    p.compare("index","indexes")    # RETURNS "s:p"
    p.compare("index","indices")    # RETURNS "s:p"
    p.compare("indexes","index")    # RETURNS "p:s"
    p.compare("indices","index")    # RETURNS "p:s"
    p.compare("indices","indexes")  # RETURNS "p:p"
    p.compare("indexes","indices")  # RETURNS "p:p"
    p.compare("indices","indices")  # RETURNS "eq"

As indicated by the comments in the previous example, the actual value
returned by the various ``compare`` methods encodes which of the
three equality rules succeeded: "eq" is returned if the strings were
identical, "s:p" if the strings were singular and plural respectively,
"p:s" for plural and singular, and "p:p" for two distinct plurals.
Inequality is indicated by returning an empty string.

It should be noted that two distinct singular words which happen to take
the same plural form are *not* considered equal, nor are cases where
one (singular) word's plural is the other (plural) word's singular.
Hence all of the following return false::

    p.compare("base","basis")       # ALTHOUGH BOTH -> "bases"
    p.compare("syrinx","syringe")   # ALTHOUGH BOTH -> "syringes"
    p.compare("she","he")           # ALTHOUGH BOTH -> "they"

    p.compare("opus","operas")      # ALTHOUGH "opus" -> "opera" -> "operas"
    p.compare("taxi","taxes")       # ALTHOUGH "taxi" -> "taxis" -> "taxes"

Note too that, although the comparison is "number-insensitive" it is *not*
case-insensitive (that is, ``plural("time","Times")`` returns false. To obtain
both number and case insensitivity, use the ``lower()`` method on both strings
(that is, ``plural("time".lower(), "Times".lower())`` returns true).


OTHER VERB FORMS
================

Present participles
-------------------

``inflect.py`` also provides the ``present_participle`` method,
which can take a 3rd person singular verb and
correctly inflect it to its present participle::

    p.present_participle("runs")   # "running"
    p.present_participle("loves")  # "loving"
    p.present_participle("eats")   # "eating"
    p.present_participle("bats")   # "batting"
    p.present_participle("spies")  # "spying"


PROVIDING INDEFINITE ARTICLES
=============================

Selecting indefinite articles
-----------------------------

inflect.py provides two methods (``a(word, count=None)`` and
``an(word, count=None)``) which will correctly prepend the appropriate indefinite
article to a word, depending on its pronunciation. For example::

    p.a("cat")        # -> "a cat"
    p.an("cat")       # -> "a cat"
    p.a("euphemism")      # -> "a euphemism"
    p.a("Euler number")   # -> "an Euler number"
    p.a("hour")       # -> "an hour"
    p.a("houri")      # -> "a houri"

The two methods are *identical* in function and may be used
interchangeably. The only reason that two versions are provided is to
enhance the readability of code such as::

    print "That is ", an(errortype), " error
    print "That is ", a(fataltype), " fatal error

Note that in both cases the actual article provided depends *only* on
the pronunciation of the first argument, *not* on the name of the
method.

``a()`` and ``an()`` will ignore any indefinite article that already
exists at the start of the string. Thus::

    half_arked = [
        "a elephant",
        "a giraffe",
        "an ewe",
        "a orangutan",
    ]

    for txt in half_arked:
        print p.a(txt)

    # prints:
    #     an elephant
    #     a giraffe
    #     a ewe
    #     an orangutan


``a()`` and ``an()`` both take an optional second argument. As with the
``plural...`` methods, this second argument is a "number" specifier. If
its value is ``1`` (or some other value implying singularity), ``a()`` and
``an()`` insert "a" or "an" as appropriate. If the number specifier 
implies plurality, (``a()`` and ``an()`` insert the actual second argument instead.
For example::

    p.a("cat",1)      # -> "a cat"
    p.a("cat",2)      # -> "2 cat"
    p.a("cat","one")      # -> "one cat"
    p.a("cat","no")       # -> "no cat"

Note that, as implied by the previous examples, ``a()`` and
``an()`` both assume that their job is merely to provide the correct
qualifier for a word (that is: "a", "an", or the specified count).
In other words, they assume that the word they are given has
already been correctly inflected for plurality. Hence, if ``N`` 
has the value 2, then::

      print p.a("cat",N)

prints "2 cat", instead of "2 cats". The correct approach is to use::

      print p.a(p.plural("cat",N),N)

or, better still::

      print p.no("cat",N)

Note too that, like the various ``plural...`` methods, whenever ``a()``
and ``an()`` are called with only one argument they are subject to the
effects of any preceding call to ``num()``. Hence, another possible
solution is::

      p.num(N)
      print p.a(p.plural("cat"))
    

Indefinite articles and initialisms
-----------------------------------

"Initialisms" (sometimes inaccurately called "acronyms") are terms which
have been formed from the initial letters of words in a phrase (for
example, "NATO", "NBL", "S.O.S.", "SCUBA", etc.)

Such terms present a particular challenge when selecting between "a"
and "an", since they are sometimes pronounced as if they were a single
word ("nay-tow", "sku-ba") and sometimes as a series of letter names
("en-eff-ell", "ess-oh-ess").

``a()`` and ``an()`` cope with this dichotomy using a series of inbuilt
rules, which may be summarized as:



 If the word starts with a single letter, followed by a period or dash
 (for example, "R.I.P.", "C.O.D.", "e-mail", "X-ray", "T-square"), then
 choose the appropriate article for the *sound* of the first letter
 ("an R.I.P.", "a C.O.D.", "an e-mail", "an X-ray", "a T-square").


 If the first two letters of the word are capitals,
 consonants, and do not appear at the start of any known English word,
 (for example, "LCD", "XML", "YWCA"), then once again choose "a" or
 "an" depending on the *sound* of the first letter ("an LCD", "an
 XML", "a YWCA").


 Otherwise, assume the string is a capitalized word or a
 pronounceable initialism (for example, "LED", "OPEC", "FAQ", "UNESCO"), and
 therefore takes "a" or "an" according to the (apparent) pronunciation of
 the entire word ("a LED", "an OPEC", "a FAQ", "a UNESCO").


Note that rules 1 and 3 together imply that the presence or absence of
punctuation may change the selection of indefinite article for a
particular initialism (for example, "a FAQ" but "an F.A.Q.").


Indefinite articles and "soft H's"
----------------------------------

Words beginning in the letter 'H' present another type of difficulty
when selecting a suitable indefinite article. In a few such words
(for example, "hour", "honour", "heir") the 'H' is not voiced at
all, and so such words inflect with "an". The remaining cases
("voiced H's") may be divided into two categories:
"hard H's" (such as "hangman", "holograph", "hat", etc.) and
"soft H's" (such as "hysterical", "horrendous", "holy", etc.)

Hard H's always take "a" as their indefinite article, and soft
H's normally do so as well. But *some* English speakers prefer
"an" for soft H's (although the practice is now generally considered an
affectation, rather than a legitimate grammatical alternative).

At present, the ``a()`` and ``an()`` methods ignore soft H's and use
"a" for any voiced 'H'. The author would, however, welcome feedback on
this decision (envisaging a possible future "soft H" mode).


INFLECTING ORDINALS
===================

Occasionally it is useful to present an integer value as an ordinal
rather than as a numeral. For example::

    Enter password (1st attempt): ********
    Enter password (2nd attempt): *********
    Enter password (3rd attempt): *********
    No 4th attempt. Access denied.

To this end, inflect.py provides the ``ordinal()`` method.
``ordinal()`` takes a single argument and forms its ordinal equivalent.
If the argument isn't a numerical integer, it just adds "-th".


CONVERTING NUMBERS TO WORDS
===========================

The method ``number_to_words`` takes a number (cardinal or ordinal)
and returns an English representation of that number.

::

    word = p.number_to_words(1234567)

puts the string::

    "one million, two hundred and thirty-four thousand, five hundred and sixty-seven"
    
into ``words``.

A list can be return where each comma-separated chunk is returned as a separate element.
Hence::

    words = p.number_to_words(1234567, wantlist=True)

puts the list::

    ["one million",
     "two hundred and thirty-four thousand",
     "five hundred and sixty-seven"]

into ``words``.

Non-digits (apart from an optional leading plus or minus sign,
any decimal points, and ordinal suffixes -- see below) are silently
ignored, so the following all produce identical results::

        p.number_to_words(5551202)
        p.number_to_words(5_551_202)
        p.number_to_words("5,551,202")
        p.number_to_words("555-1202")

That last case is a little awkward since it's almost certainly a phone number,
and "five million, five hundred and fifty-one thousand, two hundred and two"
probably isn't what's wanted.

To overcome this, ``number_to_words()`` takes an optional argument, 'group',
which changes how numbers are translated. The argument must be a
positive integer less than four, which indicated how the digits of the
number are to be grouped. If the argument is ``1``, then each digit is
translated separately. If the argument is ``2``, pairs of digits
(starting from the *left*) are grouped together. If the argument is
``3``, triples of numbers (again, from the *left*) are grouped. Hence::

        p.number_to_words("555-1202", group=1)

returns ``"five, five, five, one, two, zero, two"``, whilst::

        p.number_to_words("555-1202", group=2)

returns ``"fifty-five, fifty-one, twenty, two"``, and::

        p.number_to_words("555-1202", group=3)

returns ``"five fifty-five, one twenty, two"``.

Phone numbers are often written in words as
``"five..five..five..one..two..zero..two"``, which is also easy to
achieve::

        join '..', p.number_to_words("555-1202", group=>1)

``number_to_words`` also handles decimal fractions. Hence::

        p.number_to_words("1.2345")

returns ``"one point two three four five"`` in a scalar context
and ``("one","point","two","three","four","five")``) in an array context.
Exponent form (``"1.234e56"``) is not yet handled.

Multiple decimal points are only translated in one of the "grouping" modes.
Hence::

        p.number_to_words(101.202.303)

returns ``"one hundred and one point two zero two three zero three"``,
whereas::

        p.number_to_words(101.202.303, group=1)

returns ``"one zero one point two zero two point three zero three"``.

The digit ``'0'`` is unusual in that in may be translated to English as "zero",
"oh", or "nought". To cater for this diversity, ``number_to_words`` may be passed
a named argument, 'zero', which may be set to
the desired translation of ``'0'``. For example::

        print join "..", p.number_to_words("555-1202", group=3, zero='oh')

prints ``"five..five..five..one..two..oh..two"``.
By default, zero is rendered as "zero".

Likewise, the digit ``'1'`` may be rendered as "one" or "a/an" (or very
occasionally other variants), depending on the context. So there is a
``'one'`` argument as well::

        for num in [3,2,1,0]:
              print p.number_to_words(num, one='a solitary', zero='no more'),
              p.plural(" bottle of beer on the wall", num)

        # prints:
        #     three bottles of beer on the wall
        #     two bottles of beer on the wall
        #     a solitary bottle of beer on the wall
        #     no more bottles of beer on the wall
              
Care is needed if the word "a/an" is to be used as a ``'one'`` value.
Unless the next word is known in advance, it's almost always necessary
to use the ``A`` function as well::


        for word in ["cat aardvark ewe hour".split()]:
            print p.a("{0} {1}".format(p.number_to_words(1, one='a'), word))

    # prints:
    #     a cat
    #     an aardvark
    #     a ewe
    #     an hour

Another major regional variation in number translation is the use of
"and" in certain contexts. The named argument 'and'
allows the programmer to specify how "and" should be handled. Hence::

        print scalar p.number_to_words("765", andword='')

prints "seven hundred sixty-five", instead of "seven hundred and sixty-five".
By default, the "and" is included.

The translation of the decimal point is also subject to variation
(with "point", "dot", and "decimal" being the favorites).
The named argument 'decimal' allows the
programmer to how the decimal point should be rendered. Hence::

        print scalar p.number_to_words("666.124.64.101", group=3, decimal='dot')

prints "six sixty-six, dot, one twenty-four, dot, sixty-four, dot, one zero one"
By default, the decimal point is rendered as "point".

``number_to_words`` also handles the ordinal forms of numbers. So::

        print p.number_to_words('1st')
        print p.number_to_words('3rd')
        print p.number_to_words('202nd')
        print p.number_to_words('1000000th')

prints::

        first
        third
        two hundred and twenty-second
        one millionth

Two common idioms in this regard are::

        print p.number_to_words(ordinal(number))

and::

        print p.ordinal(p.number_to_words(number))

These are identical in effect, except when ``number`` contains a decimal::

        number = 99.09
        print p.number_to_words(p.ordinal(number));    # ninety-ninth point zero nine
        print p.ordinal(p.number_to_words(number));    # ninety-nine point zero ninth

Use whichever you feel is most appropriate.


CONVERTING LISTS OF WORDS TO PHRASES
====================================

When creating a list of words, commas are used between adjacent items,
except if the items contain commas, in which case semicolons are used.
But if there are less than two items, the commas/semicolons are omitted
entirely. The final item also has a conjunction (usually "and" or "or")
before it. And although it's technically incorrect (and sometimes
misleading), some people prefer to omit the comma before that final
conjunction, even when there are more than two items.

That's complicated enough to warrant its own method: ``join()``.
This method expects a tuple of words, possibly with one or more
options. It returns a string that joins the list
together in the normal English usage. For example::

    print "You chose ", p.join(selected_items)
    # You chose barley soup, roast beef, and Yorkshire pudding

    print "You chose ", p.join(selected_items, final_sep=>"")
    # You chose barley soup, roast beef and Yorkshire pudding

    print "Please chose ", p.join(side_orders, conj=>"or")
    # Please chose salad, vegetables, or ice-cream

The available options are::

    Option named    Specifies                Default value

    conj            Final conjunction        "and"
    sep             Inter-item separator     ","
    last_sep        Final separator          value of 'sep' option
    sep_spaced      Space follows sep        True
    conj_spaced     Spaces around conj       True


INTERPOLATING INFLECTIONS IN STRINGS
====================================

By far the commonest use of the inflection methods is to
produce message strings for various purposes. For example::

        print p.num(errors), p.plural_noun(" error"), p.plural_verb(" was"), " detected."
        if severity > 1:
            print p.plural_adj("This"), p.plural_noun(" error"), p.plural_verb(" was"), "fatal."

Unfortunately the need to separate each method call detracts
significantly from the readability of the resulting code. To ameliorate
this problem, inflect.py provides a string-interpolating
method (``inflect(txt)``), which recognizes calls to the various inflection
methods within a string and interpolates them appropriately.

Using ``inflect`` the previous example could be rewritten::

        print p.inflect("num({0}) plural_noun(error) plural_verb(was) detected.".format(errors))
        if severity > 1:
            print p.inflect("plural_adj(This) plural_noun(error) plural_verb(was) fatal.")

Note that ``inflect`` also correctly handles calls to the ``num()`` method
(whether interpolated or antecedent). The ``inflect()`` method has
a related extra feature, in that it *automatically* cancels any "default
number" value before it returns its interpolated string. This means that
calls to ``num()`` which are embedded in an ``inflect()``-interpolated
string do not "escape" and interfere with subsequent inflections.


MODERN VS CLASSICAL INFLECTIONS
===============================

Certain words, mainly of Latin or Ancient Greek origin, can form
plurals either using the standard English "-s" suffix, or with 
their original Latin or Greek inflections. For example::

        p.plural("stigma")            # -> "stigmas" or "stigmata"
        p.plural("torus")             # -> "toruses" or "tori"
        p.plural("index")             # -> "indexes" or "indices"
        p.plural("millennium")        # -> "millenniums" or "millennia"
        p.plural("ganglion")          # -> "ganglions" or "ganglia"
        p.plural("octopus")           # -> "octopuses" or "octopodes"


inflect.py caters to such words by providing an
"alternate state" of inflection known as "classical mode".
By default, words are inflected using their contemporary English
plurals, but if classical mode is invoked, the more traditional 
plural forms are returned instead.

The method ``classical()`` controls this feature.
If ``classical()`` is called with no arguments, it unconditionally
invokes classical mode. If it is called with a single argument, it
turns all classical inflects on or off (depending on whether the argument is
true or false). If called with two or more arguments, those arguments 
specify which aspects of classical behaviour are to be used.

Thus::

        p.classical()                # SWITCH ON CLASSICAL MODE
        print p.plural("formula")        # -> "formulae"

        p.classical(all=False)               # SWITCH OFF CLASSICAL MODE
        print p.plural("formula")        # -> "formulas"

        p.classical(cmode=True)           # CLASSICAL MODE IFF cmode
        print p.plural("formula")        # -> "formulae" (IF cmode)
                                     # -> "formulas" (OTHERWISE)

        p.classical(herd=True)          # SWITCH ON CLASSICAL MODE FOR "HERD" NOUNS
        print p.plural("wilderbeest")    # -> "wilderbeest"

        p.classical(names=True)         # SWITCH ON CLASSICAL MODE FOR NAMES
        print p.plural("sally")          # -> "sallies"
        print p.plural("Sally")          # -> "Sallys"

Note however that ``classical()`` has no effect on the inflection of words which
are now fully assimilated. Hence::

        p.plural("forum")             # ALWAYS -> "forums"
        p.plural("criterion")         # ALWAYS -> "criteria"

LEI assumes that a capitalized word is a person's name. So it forms the
plural according to the rules for names (which is that you don't
inflect, you just add -s or -es). You can choose to turn that behaviour
off (it's on by the default, even when the module isn't in classical
mode) by calling `` classical(names=0) ``

USER-DEFINED INFLECTIONS
========================

Adding plurals at run-time
--------------------------

inflect.py provides five methods which allow
the programmer to override the module's behaviour for specific cases:


``defnoun(singular, plural)``

 The ``defnoun`` method takes a pair of string arguments: the singular and the
 plural forms of the noun being specified. The singular form 
 specifies a pattern to be interpolated (as ``m/^(?:$first_arg)$/i``).
 Any noun matching this pattern is then replaced by the string in the
 second argument. The second argument specifies a string which is
 interpolated after the match succeeds, and is then used as the plural
 form. For example::

      defnoun( 'cow'        , 'kine')
      defnoun( '(.+i)o'     , '$1i')
      defnoun( 'spam(mer)?' , '\\$\\%\\@#\\$\\@#!!')

 Note that both arguments should usually be specified in single quotes,
 so that they are not interpolated when they are specified, but later (when
 words are compared to them). As indicated by the last example, care
 also needs to be taken with certain characters in the second argument,
 to ensure that they are not unintentionally interpolated during comparison.

 The second argument string may also specify a second variant of the plural
 form, to be used when "classical" plurals have been requested. The beginning
 of the second variant is marked by a '|' character::

      defnoun( 'cow'        , 'cows|kine')
      defnoun( '(.+i)o'     , '$1os|$1i')
      defnoun( 'spam(mer)?' , '\\$\\%\\@#\\$\\@#!!|varmints')

 If no classical variant is given, the specified plural form is used in
 both normal and "classical" modes.


..
   #TODO: check that the following paragraph is implemented

 If the second argument is ``None`` instead of a string, then the
 current user definition for the first argument is removed, and the
 standard plural inflection(s) restored.


 Note that in all cases, later plural definitions for a particular
 singular form replace earlier definitions of the same form. For example::

      # FIRST, HIDE THE MODERN FORM....
      defnoun( 'aviatrix' , 'aviatrices')

      # LATER, HIDE THE CLASSICAL FORM...
      defnoun( 'aviatrix' , 'aviatrixes')

      # FINALLY, RESTORE THE DEFAULT BEHAVIOUR...
      defnoun( 'aviatrix' , undef)


 Special care is also required when defining general patterns and
 associated specific exceptions: put the more specific cases *after*
 the general pattern. For example::

      defnoun( '(.+)us' , '$1i')      # EVERY "-us" TO "-i"
      defnoun( 'bus'    , 'buses')    # EXCEPT FOR "bus"

 This "try-most-recently-defined-first" approach to matching
 user-defined words is also used by ``defverb``, ``defa`` and ``defan``.


``defverb(s1, p1, s2, p2, s3, p3)``

 The ``defverb`` method takes three pairs of string arguments (that is, six
 arguments in total), specifying the singular and plural forms of the three
 "persons" of verb. As with ``defnoun``, the singular forms are specifications of
 run-time-interpolated patterns, whilst the plural forms are specifications of
 (up to two) run-time-interpolated strings::

       defverb('am'       , 'are',
                'are'      , 'are|art",
                'is'       , 'are')

       defverb('have'     , 'have',
                'have'     , 'have",
                'ha(s|th)' , 'have')

 Note that as with ``defnoun``, modern/classical variants of plurals
 may be separately specified, subsequent definitions replace previous
 ones, and ``None``'ed plural forms revert to the standard behaviour.


``defadj(singular, plural)``

 The ``defadj`` method takes a pair of string arguments, which specify
 the singular and plural forms of the adjective being defined.
 As with ``defnoun`` and ``defadj``, the singular forms are specifications of
 run-time-interpolated patterns, whilst the plural forms are specifications of
 (up to two) run-time-interpolated strings::

       defadj( 'this'     , 'these')
       defadj( 'red'      , 'red|gules')

 As previously, modern/classical variants of plurals
 may be separately specified, subsequent definitions replace previous
 ones, and ``None``'ed plural forms revert to the standard behaviour.


``defa(pattern)`` and ``defan(pattern)``

 The ``defa`` and ``defan`` methods each take a single argument, which
 specifies a pattern. If a word passed to ``a()`` or ``an()`` matches this
 pattern, it will be prefixed (unconditionally) with the corresponding indefinite
 article. For example::

      defa( 'error')
      defa( 'in.+')

      defan('mistake')
      defan('error')

 As with the other ``def_...`` methods, such redefinitions are sequential
 in effect so that, after the above example, "error" will be inflected with "an".


The ``<$HOME/.inflectrc`` file
------------------------------

THIS HAS NOT BEEN IMPLEMENTED IN THE PYTHON VERSION YET

When it is imported, inflect.py executes (as Perl code)
the contents of any file named ``.inflectrc`` which it finds in the
in the directory where ``Lingua/EN/Inflect.pm`` is installed,
or in the current home directory (``$ENV{HOME}``), or in both.
Note that the code is executed within the inflect.py
namespace.

Hence the user or the local Perl guru can make appropriate calls to
``defnoun``, ``defverb``, etc. in one of these ``.inflectrc`` files, to
permanently and universally modify the behaviour of the module. For example

      > cat /usr/local/lib/perl5/Text/Inflect/.inflectrc

      defnoun  "UNIX"  => "UN*X|UNICES"

      defverb  "teco"  => "teco",      # LITERALLY: "to edit with TECO"
                "teco"  => "teco",
                "tecos" => "teco"

      defa     "Euler.*";              # "Yewler" TURNS IN HIS GRAVE


Note that calls to the ``def_...`` methods from within a program
will take precedence over the contents of the home directory
F<.inflectrc> file, which in turn takes precedence over the system-wide
F<.inflectrc> file.


DIAGNOSTICS
===========

THIS HAS NOT BEEN IMPLEMENTED IN THE PYTHON VERSION YET

On loading, if the Perl code in a ``.inflectrc`` file is invalid
(syntactically or otherwise), an appropriate fatal error is issued.
A common problem is not ending the file with something that
evaluates to true (as the five ``def_...`` methods do).

Using the five ``def_...`` methods directly in a program may also
result in fatal diagnostics, if a (singular) pattern or an interpolated
(plural) string is somehow invalid.

Specific diagnostics related to user-defined inflections are:


``"Bad user-defined singular pattern:\t %s"``

 The singular form of a user-defined noun or verb
 (as defined by a call to ``defnoun``, ``defverb``, ``defadj``,
 ``defa`` or ``defan``) is not a valid Perl regular expression. The
 actual Perl error message is also given.

``"Bad user-defined plural string: '%s'"``

 The plural form(s) of a user-defined noun or verb
 (as defined by a call to ``defnoun``, ``defverb`` or ``defadj``)
 is not a valid Perl interpolated string (usually because it 
 interpolates some undefined variable).

``"Bad .inflectrc file (%s): %s"``

 Some other problem occurred in loading the named local 
 or global F<.inflectrc> file. The Perl error message (including
 the line number) is also given.


There are *no* diagnosable run-time error conditions for the actual
inflection methods, except ``number_to_words`` and hence no run-time
diagnostics. If the inflection methods are unable to form a plural
via a user-definition or an inbuilt rule, they just "guess" the
commonest English inflection: adding "-s" for nouns, removing "-s" for
verbs, and no inflection for adjectives.

``inflect.py`` can raise the following execeptions:

``BadChunkingOptionError``

 The optional argument to ``number_to_words()`` wasn't 1, 2 or 3.

``NumOutOfRangeError``

 ``number_to_words()`` was passed a number larger than
 999,999,999,999,999,999,999,999,999,999,999,999 (that is: nine hundred
 and ninety-nine decillion, nine hundred and ninety-nine nonillion, nine
 hundred and ninety-nine octillion, nine hundred and ninety-nine
 septillion, nine hundred and ninety-nine sextillion, nine hundred and
 ninety-nine quintillion, nine hundred and ninety-nine quadrillion, nine
 hundred and ninety-nine trillion, nine hundred and ninety-nine billion,
 nine hundred and ninety-nine million, nine hundred and ninety-nine
 thousand, nine hundred and ninety-nine :-) 

 The problem is that ``number_to_words`` doesn't know any
 words for number components bigger than "decillion".


..
   #TODO expand these

``UnknownClassicalModeError``

``BadNumValueError``

``BadUserDefinedPatternError``

``BadRcFileError``


OTHER ISSUES
============

2nd Person precedence
---------------------

If a verb has identical 1st and 2nd person singular forms, but
different 1st and 2nd person plural forms, then when its plural is
constructed, the 2nd person plural form is always preferred.

The author is not currently aware of any such verbs in English, but is
not quite arrogant enough to assume *ipso facto* that none exist.


Nominative precedence
---------------------

The singular pronoun "it" presents a special problem because its plural form
can vary, depending on its "case". For example::

        It ate my homework       ->  They ate my homework
        It ate it                ->  They ate them
        I fed my homework to it  ->  I fed my homework to them

As a consequence of this ambiguity, ``plural()`` or ``plural_noun`` have been implemented
so that they always return the *nominative* plural (that is, "they").

However, when asked for the plural of an unambiguously *accusative*
"it" (namely, ``plural("to it")``, ``plural_noun("from it")``, ``plural("with it")``,
etc.), both methods will correctly return the accusative plural
("to them", "from them", "with them", etc.)


The plurality of zero
---------------------

The rules governing the choice between::

      There were no errors.

and

::

      There was no error.

are complex and often depend more on *intent* rather than *content*.
Hence it is infeasible to specify such rules algorithmically.

Therefore, inflect.py contents itself with the following compromise: If
the governing number is zero, inflections always return the plural form
unless the appropriate "classical" inflection is in effect, in which case the
singular form is always returned.

Thus, the sequence::

      p.num(0)
      print p.inflect("There plural(was) no(choice)")

produces "There were no choices", whereas::

      p.classical(zero=True)
      p.num(0)
      print p.inflect("There plural(was) no(choice)")

it will print "There was no choice".


Homographs with heterogeneous plurals
-------------------------------------

Another context in which intent (and not content) sometimes determines
plurality is where two distinct meanings of a word require different
plurals. For example::

      Three basses were stolen from the band's equipment trailer.
      Three bass were stolen from the band's aquarium.

      I put the mice next to the cheese.
      I put the mouses next to the computers.

      Several thoughts about leaving crossed my mind.
      Several thought about leaving across my lawn.

inflect.py handles such words in two ways:


- If both meanings of the word are the *same* part of speech (for
  example, "bass" is a noun in both sentences above), then one meaning
  is chosen as the "usual" meaning, and only that meaning's plural is
  ever returned by any of the inflection methods.

- If each meaning of the word is a different part of speech (for
  example, "thought" is both a noun and a verb), then the noun's
  plural is returned by ``plural()`` and ``plural_noun()`` and the verb's plural is
  returned only by ``plural_verb()``.


Such contexts are, fortunately, uncommon (particularly
"same-part-of-speech" examples). An informal study of nearly 600
"difficult plurals" indicates that ``plural()`` can be relied upon to "get
it right" about 98% of the time (although, of course, ichthyophilic
guitarists or cyber-behaviouralists may experience higher rates of
confusion).

If the choice of a particular "usual inflection" is considered
inappropriate, it can always be reversed with a preliminary call
to the corresponding ``def_...`` method.

NOTE
====

There will be no further correspondence on:

"octopi".

 Despite the populist pandering of certain New World dictionaries, the
 plural is "octopuses" or (for the pendantic classicist) "octopodes". The
 suffix "-pus" is Greek, not Latin, so the plural is "-podes", not "pi".


"virus".

 Had no plural in Latin (possibly because it was a mass noun).
 The only plural is the Anglicized "viruses".


AUTHORS
=======

Paul Dyson ([email protected])
* converted code from Perl to Python
* added singular_noun functionality

Original Perl version of the code and documentation:
Damian Conway ([email protected]),
Matthew Persico (ORD inflection)


BUGS AND IRRITATIONS
====================

The endless inconsistencies of English.

(*Please* report words for which the correct plural or
indefinite article is not formed, so that the reliability
of inflect.py can be improved.)



COPYRIGHT
=========

    Copyright (C) 2010 Paul Dyson

    Based upon the Perl module Lingua::EN::Inflect by Damian Conway.

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.

    The original Perl module Lingua::EN::Inflect by Damian Conway is 
    available from http://search.cpan.org/~dconway/

    This module can be downloaded at http://pypi.python.org/pypi/inflect

    This module can be installed via ``easy_install inflect``

    Repository available at http://github.com/pwdyson/inflect.py