Set reachable depth for generate

Author: ekaf

nltk/parse/generate.py

@@ -3,6 +3,7 @@
 # Copyright (C) 2001-2023 NLTK Project
 # Author: Steven Bird <[email protected]>
 #         Peter Ljunglöf <[email protected]>
+#         Eric Kafe <[email protected]>
 # URL: <https://www.nltk.org/>
 # For license information, see LICENSE.TXT
 #
@@ -13,6 +14,13 @@
 from nltk.grammar import Nonterminal
 
 
+def is_recursive(grammar):
+    for prod in grammar.productions():
+        if prod.lhs() in prod.rhs():
+            return True
+    return False
+
+
 def generate(grammar, start=None, depth=None, n=None):
     """
     Generates an iterator of all sentences from a CFG.
@@ -26,7 +34,11 @@ def generate(grammar, start=None, depth=None, n=None):
     if not start:
         start = grammar.start()
     if depth is None:
-        depth = sys.maxsize
+        if is_recursive(grammar):
+            # This seems to be an almost maximal safe default with Python 3:
+            depth = (sys.getrecursionlimit() // 3) - 3
+        else:
+            depth = sys.maxsize
 
     iter = _generate_all(grammar, [start], depth)
 
@@ -45,7 +57,8 @@ def _generate_all(grammar, items, depth):
         except RecursionError as error:
             # Helpful error message while still showing the recursion stack.
             raise RuntimeError(
-                "The grammar has rule(s) that yield infinite recursion!"
+                "The grammar has rule(s) that yield infinite recursion!\n\
+Eventually use a lower 'depth', or a higher 'sys.setrecursionlimit()'."
             ) from error
     else:
         yield []