[util] implement 'build_duration_func_ex()'

gallery_dl/util.py

@@ -843,9 +843,7 @@ def import_file(path):
 
 def build_selection_func(value, min=0.0, conv=float):
     if not value:
-        if min:
-            return lambda: min
-        return None
+        return (lambda: min) if min else None
 
     if isinstance(value, str):
         lower, _, upper = value.partition("-")
@@ -853,7 +851,8 @@ def build_selection_func(value, min=0.0, conv=float):
         try:
             lower, upper = value
         except TypeError:
-            lower, upper = value, None
+            lower = value
+            upper = None
     lower = conv(lower)
 
     if upper:
@@ -872,6 +871,38 @@ def build_selection_func(value, min=0.0, conv=float):
 build_duration_func = build_selection_func
 
 
+def build_duration_func_ex(value):
+    if not value:
+        return None
+    if not isinstance(value, str) or "=" not in value:
+        value = build_duration_func(value)
+        return lambda _: value()
+
+    args, _, value = value.partition("=")
+    type, _, args = args.partition(":")
+    value = build_duration_func(value)
+
+    if "exponential".startswith(type):
+        if not args:
+            return lambda n: value() * (2 ** (n-1))
+        base, _, start = args.partition(":")
+        start, _, max = start.partition(":")
+        start = float(start) if start else 0
+        base = float(base) if base else 2
+        max = int(max) if max else 3600
+        return lambda n: min(start + value() * (base ** (n-1)), max)
+
+    if "linear".startswith(type):
+        if not args:
+            return lambda n: value() * n
+        start, _, max = args.partition(":")
+        start = float(start) if start else 0
+        max = int(max) if max else 3600
+        return lambda n: min(start + value() * n, max)
+
+    raise ValueError("Invalid duration type " + repr(type))
+
+
 def build_extractor_filter(categories, negate=True, special=None):
     """Build a function that takes an Extractor class as argument
     and returns True if that class is allowed by 'categories'

test/test_util.py

@@ -1,7 +1,7 @@
 #!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
-# Copyright 2015-2025 Mike Fährmann
+# Copyright 2015-2026 Mike Fährmann
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 2 as
@@ -613,10 +613,64 @@ value = 123
         test_single(f("3", 0, pb)     , 3, int)
         test_single(f("3.0-", 0, pb)  , 3, int)
         test_single(f("  3  -", 0, pb), 3, int)
-
         test_range(f("2k-4k", 0, pb)        , 2048, 4096, int)
         test_range(f("  2.0k  - 4k ", 0, pb), 2048, 4096, int)
 
+    def test_build_duration_func_ex(self, f=util.build_duration_func_ex):
+
+        def test(v, a, b=None):
+            df = f(v)
+            if "=" in v:
+                if b is None:
+                    for n, a in enumerate(a, 1):
+                        self.assertEqual(df(n), a)
+                else:
+                    for n, (a, b) in enumerate(zip(a, b), 1):
+                        v = df(n)
+                        self.assertGreaterEqual(v, a)
+                        self.assertLessEqual(v, b)
+            else:
+                if b is None:
+                    for n in range(10):
+                        self.assertEqual(df(n), a)
+                else:
+                    for n in range(10):
+                        v = df(n)
+                        self.assertGreaterEqual(v, a)
+                        self.assertLessEqual(v, b)
+
+        for v in (0, 0.0, "", None, (), []):
+            self.assertIsNone(f(v))
+
+        test("3", 3.0)
+        test("3-5", 3.0, 5.0)
+
+        test("lin=3"     , ( 3, 6, 9, 12, 15))   # noqa E201
+        test("lin:8=3"  , (11, 14, 17, 20, 23))
+        test("lin:8:20=5", (13, 18, 20, 20, 20))
+        test("lin=2-5"     ,
+             (2,  4,  6,  8, 10),  # noqa E241
+             (5, 10, 15, 20, 25))
+        test("lin:8=2-5"   ,
+             (10, 12, 14, 16, 18),
+             (13, 18, 23, 28, 33))
+        test("lin:8:20=2-5",
+             (10, 12, 14, 16, 18),
+             (13, 18, 20, 20, 20))
+
+        test("exp=3"       , (3*1, 3*2, 3*4, 3*8, 3*16))
+        test("exp:1.5=3"   , (3*1, 3*1.5, 3*1.5**2, 3*1.5**3))
+        test("exp::20:40=3", (23, 26, 32, 40, 40))
+        test("exp=2-4"    ,
+             (2*1, 2*2, 2*4, 2*8, 2*16),
+             (4*1, 4*2, 4*4, 4*8, 4*16))
+        test("exp:3=2-4"  ,
+             (2*1, 2*3, 2*9, 2*27, 2*81),
+             (4*1, 4*3, 4*9, 4*27, 4*81))
+        test("exp:3::40=2-4",
+             (2*1, 2*3, 2*9, 40, 40),
+             (4*1, 4*3,  40, 40, 40))  # noqa E241
+
     def test_extractor_filter(self):
         # empty
         func = util.build_extractor_filter("")