Plural String Formatting

Using custom formatter:

import string

class PluralFormatter(string.Formatter):
    def get_value(self, key, args, kwargs):
        if isinstance(key, int):
            return args[key]
        if key in kwargs:
            return kwargs[key]
        if '(' in key and key.endswith(')'):
            key, rest = key.split('(', 1)
            value = kwargs[key]
            suffix = rest.rstrip(')').split(',')
            if len(suffix) == 1:
                suffix.insert(0, '')
            return suffix[0] if value <= 1 else suffix[1]
        else:
            raise KeyError(key)

data = {'tree': 1, 'bush': 2, 'flower': 3, 'cactus': 0}
formatter = PluralFormatter()
fmt = "{tree} tree{tree(s)}, {bush} bush{bush(es)}, {flower} flower{flower(s)}, {cactus} cact{cactus(i,us)}"
print(formatter.format(fmt, **data))

Output:

1 tree, 2 bushes, 3 flowers, 0 cacti

UPDATE

If you're using Python 3.2+ (str.format_map was added), you can use the idea of OP (see comment) that use customized dict.

class PluralDict(dict):
    def __missing__(self, key):
        if '(' in key and key.endswith(')'):
            key, rest = key.split('(', 1)
            value = super().__getitem__(key)
            suffix = rest.rstrip(')').split(',')
            if len(suffix) == 1:
                suffix.insert(0, '')
            return suffix[0] if value <= 1 else suffix[1]
        raise KeyError(key)

data = PluralDict({'tree': 1, 'bush': 2, 'flower': 3, 'cactus': 0})
fmt = "{tree} tree{tree(s)}, {bush} bush{bush(es)}, {flower} flower{flower(s)}, {cactus} cact{cactus(i,us)}"
print(fmt.format_map(data))

Output: same as above.

Check out the inflect package. It will pluralize things, as well as do a whole host of other linguistic trickery. There are too many situations to special-case these yourself!

From the docs at the link above:

import inflect
p = inflect.engine()

# 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))

For your specific example:

{print(str(count) + " " + p.pluralize(string, count)) for string, count in data.items() }

If you happen to use Django already, it is easy: pluralize is a function that.

It is often used in templates:

You have {{ num_messages }} message{{ num_messages|pluralize }}.

However, you can also use it in your python code:

f'You have {num_messages} message{pluralize(num_messages)}.'

In Python2 this would read:

'You have {} message{}.'.format(num_messages, pluralize(num_messages))

or:

'You have %d message%s' % (num_messages, pluralize(num_messages))

Django pluralize docs: https://docs.djangoproject.com/en/2.0/ref/templates/builtins/#pluralize

I would go with something like

class Pluralizer:
    def __init__(self, value):
        self.value = value

    def __format__(self, formatter):
        formatter = formatter.replace("N", str(self.value))
        start, _, suffixes = formatter.partition("/")
        singular, _, plural = suffixes.rpartition("/")

        return "{}{}".format(start, singular if self.value == 1 else plural)

"There are {:N thing/s} which are made of {:/a cactus/N cacti}".format(Pluralizer(10), Pluralizer(1))
#>>> 'There are 10 things which are made of a cactus'

The format is always/singular/plural, which singular (then plural) optional.

So

"xyz/foo/bar".format(Pluralizer(1)) == "xyzfoo"
"xyz/foo/bar".format(Pluralizer(2)) == "xyzbar"

"xyz/bar".format(Pluralizer(1)) == "xyz"
"xyz/bar".format(Pluralizer(2)) == "xyzbar"

"xyz".format(Pluralizer(1)) == "xyz"
"xyz".format(Pluralizer(2)) == "xyz"

Then for your example one just does:

data = {'tree': 1, 'bush': 2, 'flower': 3, 'cactus': 0}
string = 'My garden has {tree:N tree/s}, {bush:N bush/es}, {flower:N flower/s}, and {cactus:N cact/us/i}'

string.format_map({k: Pluralizer(v) for k, v in data.items()})
#>>> 'My garden has 1 tree, 2 bushes, 3 flowers, and 0 cacti'

I was inspired by the answers above, particularly @Veedrac's, to create a Plurality utility:

https://gist.github.com/elidchan/40baea13bb91193a326e3a8c4cbcaeb9

Features:

• Customizable number-indexed templates (e.g. see 'vague' below)
• Numbers and support for $n template tokens
• Singular/plural forms (e.g. 'cact/us/i') and support for $thing/$things template tokens
• Indefinite article capability (inspired by https://stackoverflow.com/a/20337527/4182210) and support for $a template token
• Left/right string concatenation
• Partials with any subset of number, forms, and templates
• Partial completion via call() or format string

From the docstring:

"""
Usage:

>>> from utils.verbiage import Plurality

>>> f"We have {Plurality(0, 'g/oose/eese')}."
'We have 0 geese.'
>>> f"We have {Plurality(1, 'g/oose/eese')}."
'We have 1 goose.'
>>> f"We have {Plurality(2, 'g/oose/eese')}."
'We have 2 geese.'

>>> oxen = Plurality('ox/en')
>>> oxen.template_formatter
'1=$n $thing;n=$n $things'
>>> f"We have {oxen(0)}."
'We have 0 oxen.'
>>> f"We have {oxen(1)}."
'We have 1 ox.'
>>> f"We have {oxen(2)}."
'We have 2 oxen.'

>>> cows = Plurality('/cow/kine', '0=no $things', '1=$a $thing')
>>> cows.template_formatter
'0=no $things;1=a $thing;n=$n $things'
>>> f"We have {cows(0)}."
'We have no kine.'
>>> f"We have {cows(1)}."
'We have a cow.'
>>> f"We have {cows(2)}."
'We have 2 kine.'

>>> 'We have {:0=no $things;0.5=half $a $thing}.'.format(Plurality(0, 'octop/us/odes'))
'We have no octopodes.'
>>> 'We have {:octop/us/odes;0=no $things;0.5=half $a $thing}.'.format(Plurality(0.5))
'We have half an octopus.'
>>> 'We have {:4;octop/us/odes;0=no $things;0.5=half $a $thing}.'.format(Plurality())
'We have 4 octopodes.'

>>> data = {'herb': 1, 'bush': 2, 'flower': 3, 'cactus': 0}
>>> s = "We have {herb:herb/s}, {bush:bush/es}, {flower:flower/s}, and {cactus:cact/us/i}."
>>> s.format_map({k: Plurality(v) for k, v in data.items()})
'We have 1 herb, 2 bushes, 3 flowers, and 0 cacti.'
>>> vague = Plurality('0=no $things;1=$a $thing;2=a couple $things;n=some $things')
>>> s.format_map({k: vague(v) for k, v in data.items()})
'We have an herb, a couple bushes, some flowers, and no cacti.'
"""