Django template context placeholder

django_context_placeholder.py

import uuid
import datetime
import itertools
import re
import inflection # requires python library inflection (pip install inflection)


class ContextPlaceholder:
    counter = itertools.count()
    DEFAULT_VALUES = {
        'pk': lambda: next(ContextPlaceholder.counter),
        'id': lambda: next(ContextPlaceholder.counter),
        'date': datetime.date.today,
        'time': datetime.datetime.now,
        'email': "user@example.edu",
        'uuid': uuid.uuid4,
        'uid': uuid.uuid4,
        'guid': uuid.uuid4,
    }
    CHILD_VALUES = [
        'capitalize',
        'lower',
        'strip',
        'title',
        'upper',
    ]
    def __init__(self, label, parent_label=None, length=3, **extra):
        self.label = label
        self.singular_label = inflection.singularize(label)
        self.parent_label = parent_label
        self.length = length
        self.ctx = dict(self.DEFAULT_VALUES)
        self.ctx.update({k:v for k, v in extra.items() if v})
    def __repr__(self):
        return '<{}{} (as ContextPlaceHolder)>'.format(
            inflection.camelize(self.parent_label) + ':' if self.parent_label else '', 
            inflection.camelize(self.label)
        )
    def __str__(self):
        if self.label in self.CHILD_VALUES and self.parent_label:
            return getattr(inflection.camelize(str(self.parent_label)), self.label)()
        return inflection.camelize(str(self.label))
    def __iter__(self):
        return iter(
            ContextPlaceholder('{}_{}'.format(self.singular_label, idx), parent_label=self.label, length=self.length, **self.ctx)
            for idx in range(self.length)
        )
    def items(self):
        return zip(self.keys(), self.values())
    def keys(self):
        return ['{}_{}'.format(self.singular_label, idx) for idx in range(self.length)]
    def values(self):
        return [ContextPlaceholder('{}_{}'.format(self.singular_label, idx), parent_label=self.label, length=self.length, **self.ctx) for idx in range(self.length)]
    def __getitem__(self, idx):
        if isinstance(idx, slice):
            return list(self)[idx]
        try:
            idx = int(idx)
        except (TypeError, ValueError):
            pass
        try:
            return self.get_existing_value(idx)
        except KeyError:
            pass
        return ContextPlaceholder('{}_{}'.format(self.singular_label, idx), parent_label=self.label, length=self.length, **self.ctx)
    def __call__(self, *args, **kwargs):
        all_ctx = dict(self.ctx.items())
        all_ctx.update(kwargs)
        each_label = self.singular_label
        if self.label in self.CHILD_VALUES:
            return getattr(inflection.camelize(str(self.parent_label)), self.label)()
        return ContextPlaceholder('{}_instance'.format(self.singular_label), parent_label=self.label, **all_ctx)
    def __getattr__(self, key):
        return self.get_value(key)
    def get_existing_value(self, key):
        val = self.ctx[key]
        if callable(val):
            try:
                return val()
            except Exception as err:
                pass
        return val
    def get_value(self, label):
        try:
            return self.get_existing_value(label)
        except KeyError:
            pass
        if 'date_' in label or '_date' in label:
            return self.get_existing_value('date')
        if 'time_' in label or '_time' in label:
            return self.get_existing_value('time')
        if label in ('slug'):
            return inflection.dasherize(self.label)
        if label in ('url'):
            return 'https://example.com/{}{}'.format(
                re.sub(r'[_\W]+', '/', self.parent_label) + '/' if self.parent_label else '',
                re.sub(r'[_\W]+', '/', self.label)
            )
        if label in ('all', 'filter'):
            label = self.singular_label
        return ContextPlaceholder(label, parent_label=self.label, length=self.length, **self.ctx)
    def __len__(self):
        return self.length