Remove django-shorturls with my own implementation, since it's incompatible with Django 2 and unmaintained

lemonshort/__init__.py

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+default_app_config = 'lemonshort.apps.LemonshortConfig'

lemonshort/apps.py

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+from django.apps import AppConfig
+
+
+class LemonshortConfig(AppConfig):
+    name = 'lemonshort'

lemonshort/convert.py

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+from baseconv import BaseConverter
+from string import ascii_lowercase, ascii_uppercase
+
+# We have to create this collection ourselves because we want uppercase then
+# lowercase, and string.ascii_letters is lowercase then uppercase.
+chars = ascii_uppercase + ascii_lowercase
+conv = BaseConverter(chars)
+
+
+def abc_to_id(abc):
+    return int(conv.decode(abc))
+
+
+def id_to_abc(id):
+    return conv.encode(id)

lemonshort/short_url.py

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+from django.apps import apps
+from django.conf import settings
+
+from .convert import id_to_abc
+
+prefixes = {}
+
+
+def short_url(entity):
+    if not prefixes:
+        for k, m in settings.SHORTEN_MODELS.items():
+            prefixes[apps.get_model(m)] = k
+    base = '/'
+    if hasattr(settings, 'SHORT_BASE_URL'):
+        base = settings.SHORT_BASE_URL
+    return base + prefixes[type(entity)] + id_to_abc(entity.id)

lemonshort/tests/convert.py

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+from .. import convert
+
+
+def test_abc_to_id():
+    samples = {
+        'A': 0,
+        'B': 1,
+        'Y': 24,
+        'a': 26,
+        'b': 27,
+        'y': 50,
+        'BA': 52,
+        'BAB': 2705,
+    }
+    for abc, id in samples.items():
+        assert convert.abc_to_id(abc) == id
+
+
+def test_id_to_abc():
+    samples = {
+        1: 'B',
+        24: 'Y',
+        26: 'a',
+        52: 'BA',
+        78: 'Ba',
+        104: 'CA',
+        130: 'Ca',
+    }
+    for id, abc in samples.items():
+        assert convert.id_to_abc(id) == abc

lemonshort/urls.py

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+from django.conf import settings
+from django.conf.urls import url
+
+from .views import unshort
+
+app_name = 'lemonshort'
+urlpatterns = tuple(
+    url(r'^{0!s}(?P<tiny>\w+)$'.format(k), unshort, kwargs={'model': m})
+    for k, m in settings.SHORTEN_MODELS.items()
+)

lemonshort/views.py

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+from django.apps import apps
+from django.shortcuts import get_object_or_404, redirect
+
+from .convert import abc_to_id
+
+
+def unshort(request, model, tiny):
+    entity = get_object_or_404(apps.get_model(model), pk=abc_to_id(tiny))
+    return redirect(entity, permanent=True)