From fa1e212dad5e375b1b0effc9a2f0a3a70cabbb52 Mon Sep 17 00:00:00 2001
From: AC <ac@fabtek.cn>
Date: Mon, 12 Oct 2026 11:37:59 +0800
Subject: [PATCH] py: fix explicit string split limits and empty separators

---
 py/string.go       | 11 +++++++++--
 py/string_test.go  | 33 +++++++++++++++++++++++++++++++++
 py/tests/string.py |  5 +++++
 3 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/py/string.go b/py/string.go
index f88d6524..0b52705d 100644
--- a/py/string.go
+++ b/py/string.go
@@ -695,7 +695,7 @@ func (s String) find(args Tuple) (Object, error) {
 func (s String) Split(args Tuple, kwargs StringDict) (Object, error) {
 	var (
 		pyval Object = None
-		pymax Object = Int(-2)
+		pymax Object = Int(-1)
 		pyfmt        = "|Oi:split"
 		kwlst        = []string{"sep", "maxsplit"}
 	)
@@ -710,7 +710,14 @@ func (s String) Split(args Tuple, kwargs StringDict) (Object, error) {
 	)
 	switch v := pyval.(type) {
 	case String:
-		vs = strings.SplitN(string(s), string(v), int(max)+1)
+		if v == "" {
+			return nil, ExceptionNewf(ValueError, "empty separator")
+		}
+		n := -1
+		if max >= 0 && max < Int(len(s)) {
+			n = int(max) + 1
+		}
+		vs = strings.SplitN(string(s), string(v), n)
 	case NoneType:
 		vs = fieldsN(string(s), int(max))
 	default:
diff --git a/py/string_test.go b/py/string_test.go
index 053cd781..9ff54f29 100644
--- a/py/string_test.go
+++ b/py/string_test.go
@@ -144,3 +144,36 @@ func TestStringLower(t *testing.T) {
 		})
 	}
 }
+
+func TestStringSplitLimits(t *testing.T) {
+	for _, limit := range []Int{-100, -2, -1, 0, 1, 2, Int(^uint(0) >> 1)} {
+		got, err := String("a,b,c").Split(Tuple{String(","), limit}, nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+		want := Tuple{String("a"), String("b"), String("c")}
+		if limit == 0 {
+			want = Tuple{String("a,b,c")}
+		} else if limit == 1 {
+			want = Tuple{String("a"), String("b,c")}
+		}
+		items := got.(*List).Items
+		if len(items) != len(want) {
+			t.Errorf("limit %d: got %v, want %v", limit, items, want)
+			continue
+		}
+		for i := range want {
+			if items[i] != want[i] {
+				t.Errorf("limit %d: got %v, want %v", limit, items, want)
+			}
+		}
+	}
+	for _, s := range []String{"", "abc"} {
+		for _, limit := range []Int{-1, 0, 1} {
+			_, err := s.Split(Tuple{String(""), limit}, nil)
+			if !IsException(ValueError, err) {
+				t.Errorf("%q split empty with limit %d: %v, want ValueError", s, limit, err)
+			}
+		}
+	}
+}
diff --git a/py/tests/string.py b/py/tests/string.py
index d71e8645..8b6e9e78 100644
--- a/py/tests/string.py
+++ b/py/tests/string.py
@@ -112,6 +112,11 @@ class C():
 
 doc="split"
 assert ["0","1","2","4"] == list("0,1,2,4".split(","))
+assert ['a', 'b', 'c'] == 'a,b,c'.split(',', -1)
+assert ['a,b,c'] == 'a,b,c'.split(',', 0)
+assert ['a', 'b', 'c'] == 'a,b,c'.split(',', 2147483647)
+assertRaisesText(ValueError, "empty separator", lambda: 'abc'.split(''))
+assertRaisesText(ValueError, "empty separator", lambda: ''.split('', 0))
 assert [""] == list("".split(","))
 assert ['a', 'd,c'] == list("a,d,c".split(",",1))
 assert ['a', 'd', 'b'] == list(" a   d   b   ".split())