gh-109747: Improve errors for unsupported look-behind patterns (GH-109859)

Now re.error is raised instead of OverflowError or RuntimeError for
too large width of look-behind pattern.

The limit is increased to 2**32-1 (was 2**31-1).

1 files changed, 3 insertions, 1 deletions

diff --git a/Lib/re/_compiler.py b/Lib/re/_compiler.py
index d0a4c55caf6..f87712d6d6f 100644
--- a/Lib/re/_compiler.py
+++ b/Lib/re/_compiler.py
@@ -147,6 +147,8 @@ def _compile(code, pattern, flags):
                 emit(0) # look ahead
             else:
                 lo, hi = av[1].getwidth()
+                if lo > MAXCODE:
+                    raise error("looks too much behind")
                 if lo != hi:
                     raise error("look-behind requires fixed-width pattern")
                 emit(lo) # look behind
@@ -547,7 +549,7 @@ def _compile_info(code, pattern, flags):
     else:
         emit(MAXCODE)
         prefix = prefix[:MAXCODE]
-    emit(min(hi, MAXCODE))
+    emit(hi)
     # add literal prefix
     if prefix:
         emit(len(prefix)) # length