python - Plural String Formatting

Question

Given a dictionary of ints, I'm trying to format a string with each number, and a pluralization of the item.

Sample input dict:

data = {'tree': 1, 'bush': 2, 'flower': 3, 'cactus': 0}

Sample output str:

'My garden has 1 tree, 2 bushes, 3 flowers, and 0 cacti'

It needs to work with an arbitrary format string.

The best solution I've come up with is a PluralItem class to store two attributes, n (the original value), and s (the string 's' if plural, empty string '' if not). Subclassed for different pluralization methods

class PluralItem(object):
    def __init__(self, num):
        self.n = num
        self._get_s()
    def _get_s(self):
        self.s = '' if self.n == 1 else 's'

class PluralES(PluralItem):
    def _get_s(self):
        self.s = 's' if self.n == 1 else 'es'

class PluralI(PluralItem):
    def _get_s(self):
        self.s = 'us' if self.n == 1 else 'i'

Then make a new dict through comprehension and a classes mapping:

classes = {'bush': PluralES, 'cactus': PluralI, None: PluralItem}
plural_data = {key: classes.get(key, classes[None])(value) for key, value in data.items()}

Lastly, the format string, and implementation:

formatter = 'My garden has {tree.n} tree{tree.s}, {bush.n} bush{bush.s}, {flower.n} flower{flower.s}, and {cactus.n} cact{cactus.s}'
print(formatter.format(**plural_data))

Outputs the following:

My garden has 1 tree, 2 bushes, 3 flowers, and 0 cacti

For such an undoubtedly common need, I'm hesitant to throw in the towel with such a convoluted solution.

Is there a way to format a string like this using the built-in format method, and minimal additional code? Pseudocode might be something like:

"{tree} tree{tree(s)}, {bush} bush{bush(es)}, {flower} flower{flower(s)}, {cactus} cact{cactus(i,us)}".format(data)

where parentheses return the contents if value is plural, or if contents has comma, means plural/singular

What do you say to this? stackoverflow.com/questions/9244909/… — Aaron Hall♦
That's essentially what my class is doing, but I can't figure out how to put something like that in the string formatting. Especially with multiple keys. — mhlester
yeah, for my code you'd have to make yet another subclass to replace the whole word. hence the search for a better way — mhlester
For serious, I would wager there is something like 100 special cases you have to handle. See the answer below. — meawoppl

falsetru falsetru · Accepted Answer · 2014-02-19T06:27:13

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.

python - Plural String Formatting

7 Answers