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THE SOFTWARE.

percentage.py

# (c) PSP UK Group Ltd. <hello@psp-group.co.uk>
#
# For the full copyright and license information,
# please view the LICENSE file that was distributed with this source code.

import math

from jinja2.exceptions import FilterArgumentError

class FilterModule(object):
    """ Jinja2 filter for calculating percentages of a value. """

    def percentage(self, value, percentage, precision=0, method='common', as_int=True, default=0):
        """ Calculate a percentage of a value, see Jinja2 round filter. """
        if not method in ('common', 'ceil', 'floor'):
            raise FilterArgumentError('method must be common, ceil or floor')
        if percentage < 1:
            percentage = (float(percentage) * 100.00)
        try:
            result = ((float(value) / 100.0) * float(percentage))
        except (TypeError, ValueError):
            return default
        if method == 'common':
            result = round(result, precision)
        else:
            func = getattr(math, method)
            result = func(result * (10 ** precision)) / (10 ** precision)
        if as_int:
            try:
                result = int(result)
            except (TypeError, ValueError):
                # this quirk is necessary so that "42.23"|int gives 42.
                try:
                    result = int(float(result))
                except (TypeError, ValueError):
                    return default
        return result

    def filters(self):
        """ Export filters from this class to Jinja2/Ansible. """
        return {
            'percentage': self.percentage,
        }

USAGE.md

$ export ANSIBLE_FILTER_PLUGINS="./path_to_filter_plugins/"
$ ansible-playbook app.yml --inventory-file=inventory.ini [..]

# {{{ MySQL

mysql_max_memory: 8192

# MySQL, recommendations by MySQLTuner.
#
mysql_query_cache_size: "{{ mysql_max_memory | percentage(20) }}M"
mysql_innodb_buffer_pool_size: "{{ mysql_max_memory | percentage(80) }}M"

# }}}

# }}}