implement convenience wrapper for text.extract functionality

gallery_dl/text.py

@@ -149,6 +149,20 @@ def extract_iter(txt, begin, end, pos=0):
         return
 
 
+def extract_from(txt, pos=0, default=""):
+    """Returns a function object that extracts from 'txt'"""
+    def extr(begin, end, index=txt.index, txt=txt):
+        nonlocal pos
+        try:
+            first = index(begin, pos) + len(begin)
+            last = index(end, first)
+            pos = last + len(end)
+            return txt[first:last]
+        except (ValueError, TypeError, AttributeError):
+            return default
+    return extr
+
+
 def parse_bytes(value, default=0, suffixes="bkmgtp"):
     """Convert a bytes-amount ("500k", "2.5M", ...) to int"""
     try:

test/test_text.py

@@ -235,6 +235,23 @@ class TestText(unittest.TestCase):
         self.assertEqual(
             g(txt, "[", "]", 6), ["a", "d"])
 
+    def test_extract_from(self, f=text.extract_from):
+        txt = "[c][b][a]: xyz! [d][e"
+
+        e = f(txt)
+        self.assertEqual(e("[", "]"), "c")
+        self.assertEqual(e("[", "]"), "b")
+        self.assertEqual(e("[", "]"), "a")
+        self.assertEqual(e("[", "]"), "d")
+        self.assertEqual(e("[", "]"), "")
+        self.assertEqual(e("[", "]"), "")
+
+        e = f(txt, pos=6, default="END")
+        self.assertEqual(e("[", "]"), "a")
+        self.assertEqual(e("[", "]"), "d")
+        self.assertEqual(e("[", "]"), "END")
+        self.assertEqual(e("[", "]"), "END")
+
     def test_parse_bytes(self, f=text.parse_bytes):
         self.assertEqual(f("0"), 0)
         self.assertEqual(f("50"), 50)