simplify if statements by using walrus operators (#7671)

gallery_dl/extractor/__init__.py

@@ -235,8 +235,7 @@ modules = [
 def find(url):
     """Find a suitable extractor for the given URL"""
     for cls in _list_classes():
-        match = cls.pattern.match(url)
-        if match:
+        if match := cls.pattern.match(url):
             return cls(match)
     return None
 
@@ -251,8 +250,7 @@ def add(cls):
 
 def add_module(module):
     """Add all extractors in 'module' to the list of available extractors"""
-    classes = _get_classes(module)
-    if classes:
+    if classes := _get_classes(module):
         if isinstance(classes[0].pattern, str):
             for cls in classes:
                 cls.pattern = re_compile(cls.pattern)