add 'default' argument to 'text.extr()'

gallery_dl/text.py

@@ -120,13 +120,13 @@ def extract(txt, begin, end, pos=0):
         return None, pos
 
 
-def extr(txt, begin, end):
+def extr(txt, begin, end, default=""):
     """Stripped-down version of 'extract()'"""
     try:
         first = txt.index(begin) + len(begin)
         return txt[first:txt.index(end, first)]
     except (ValueError, TypeError, AttributeError):
-        return ""
+        return default
 
 
 def rextract(txt, begin, end, pos=-1):

test/test_text.py

@@ -210,6 +210,11 @@ class TestText(unittest.TestCase):
         self.assertEqual(f(txt, "<", ">"), "a")
         self.assertEqual(f(txt, "><", ">"), "b")
 
+        # 'default' argument
+        self.assertEqual(f(txt, "<", "X", None), None)
+        self.assertEqual(f(txt, "<", "X", default=None), None)
+        self.assertEqual(f(txt, "<", "X", default=()), ())
+
         # invalid arguments
         for value in INVALID:
             self.assertEqual(f(value, "<"  , ">")  , "")