Python 3.7 compatibility fix.

mentions/config.py

@@ -3,7 +3,7 @@
 from urllib.parse import urljoin
 
 from mentions import options
-from mentions.util import get_domain
+from mentions.util import compatibility, get_domain
 
 
 def base_url() -> str:
@@ -97,8 +97,8 @@ def _domain_in_set(domain: str, domains: Set[str]) -> bool:
             return True
 
         if d.startswith("*."):
-            root_domain = d.removeprefix("*.")
-            remaining_prefix = domain.removesuffix(root_domain)
+            root_domain = compatibility.removeprefix(d, "*.")
+            remaining_prefix = compatibility.removesuffix(domain, root_domain)
             if remaining_prefix == "" or remaining_prefix.endswith("."):
                 return True
 

mentions/util/compatibility.py

@@ -0,0 +1,21 @@
+"""Backport features of newer Python releases than our minimum target version.
+
+All functions should contain information about their standard library equivalent
+and the Python version in which it becomes available.
+
+These should be removed and replaced with standard library equivalents when
+we update our minimum target version."""
+
+
+def removeprefix(text: str, prefix: str) -> str:
+    """Backport of `str.removeprefix` introduced in Python 3.9"""
+    if text.startswith(prefix):
+        return text[len(prefix) :]
+    return text
+
+
+def removesuffix(text: str, suffix: str) -> str:
+    """Backport of `str.removesuffix` introduced in Python 3.9"""
+    if text.endswith(suffix):
+        return text[: -len(suffix)]
+    return text

tests/tests/test_util/test_compatibility.py

@@ -0,0 +1,22 @@
+from mentions.util.compatibility import removeprefix, removesuffix
+from tests.tests.util.testcase import SimpleTestCase
+
+
+class CompatibilityTests(SimpleTestCase):
+    def test_str_removeprefix(self):
+        func = removeprefix
+        self.assertEqual(func("abcde", "ab"), "cde")
+        self.assertEqual(func("1248", "1"), "248")
+
+        self.assertEqual(func("abcde", "bc"), "abcde")
+        self.assertEqual(func("abcde", "de"), "abcde")
+        self.assertEqual(func("abcde", "abcdef"), "abcde")
+
+    def test_str_removesuffix(self):
+        func = removesuffix
+        self.assertEqual(func("abcde", "de"), "abc")
+        self.assertEqual(func("1248", "248"), "1")
+
+        self.assertEqual(func("abcde", "ab"), "abcde")
+        self.assertEqual(func("abcde", "abcd"), "abcde")
+        self.assertEqual(func("abcde", "abcdef"), "abcde")