gh-35882: avoid messing with the recursion limit
    
Fixes #35803.
    
URL: #35882
Reported by: Marc Mezzarobba
Reviewer(s): Frédéric Chapoton

Author: Release Manager

src/sage/functions/transcendental.py

@@ -17,6 +17,7 @@
 # ****************************************************************************
 import sys
 
+from sage.misc.misc import increase_recursion_limit
 from sage.rings.integer_ring import ZZ
 from sage.rings.real_mpfr import RR
 from sage.rings.real_double import RDF
@@ -551,9 +552,8 @@ def _eval_(self, x):
             max = x.parent()(1.1)*x + 10
             abs_prec = (-self.approximate(max).log2() + rel_prec + 2*max.log2()).ceil()
             self._f = {}
-            if sys.getrecursionlimit() < max + 10:
-                sys.setrecursionlimit(int(max) + 10)
-            self._compute_power_series(max.floor(), abs_prec, cache_ring=x.parent())
+            with increase_recursion_limit(int(max)):
+                self._compute_power_series(max.floor(), abs_prec, cache_ring=x.parent())
         return self._f[n](2*(x-n-x.parent()(0.5)))
 
     def power_series(self, n, abs_prec):

src/sage/interfaces/sympy.py

@@ -1016,7 +1016,7 @@ def _sympysage_true(self):
 
 
 #------------------------------------------------------------------
-from sage.repl.ipython_extension import run_once
+from sage.misc.misc import run_once
 
 @run_once
 def sympy_init():

src/sage/misc/misc.py

@@ -38,8 +38,11 @@
 #                  https://www.gnu.org/licenses/
 # ****************************************************************************
 
+import contextlib
+import functools
 import os
 import pdb
+import sys
 import warnings
 
 from .lazy_string import lazy_string
@@ -1132,3 +1135,68 @@ def inject_variable_test(name, value, depth):
         inject_variable(name, value)
     else:
         inject_variable_test(name, value, depth - 1)
+
+
+# from https://stackoverflow.com/questions/4103773/efficient-way-of-having-a-function-only-execute-once-in-a-loop
+def run_once(func):
+    """
+    Runs a function (successfully) only once.
+
+    The running can be reset by setting the ``has_run`` attribute to False
+
+    TESTS::
+
+        sage: from sage.repl.ipython_extension import run_once
+        sage: @run_once
+        ....: def foo(work):
+        ....:     if work:
+        ....:         return 'foo worked'
+        ....:     raise RuntimeError("foo didn't work")
+        sage: foo(False)
+        Traceback (most recent call last):
+        ...
+        RuntimeError: foo didn't work
+        sage: foo(True)
+        'foo worked'
+        sage: foo(False)
+        sage: foo(True)
+    """
+    @functools.wraps(func)
+    def wrapper(*args, **kwargs):
+        if not wrapper.has_run:
+            result = func(*args, **kwargs)
+            wrapper.has_run = True
+            return result
+    wrapper.has_run = False
+    return wrapper
+
+
+@contextlib.contextmanager
+def increase_recursion_limit(increment):
+    r"""
+    Context manager to temporarily change the Python maximum recursion depth.
+
+    INPUT:
+
+    - `increment`: increment to add to the current limit
+
+    EXAMPLES::
+
+        sage: from sage.misc.misc import increase_recursion_limit
+        sage: def rec(n): None if n == 0 else rec(n-1)
+        sage: rec(10000)
+        Traceback (most recent call last):
+        ...
+        RecursionError: maximum recursion depth exceeded...
+        sage: with increase_recursion_limit(10000): rec(10000)
+        sage: rec(10000)
+        Traceback (most recent call last):
+        ...
+        RecursionError: maximum recursion depth exceeded...
+    """
+    old_limit = sys.getrecursionlimit()
+    sys.setrecursionlimit(old_limit + increment)
+    try:
+        yield
+    finally:
+        sys.setrecursionlimit(old_limit)

src/sage/repl/ipython_extension.py

@@ -68,6 +68,7 @@
 from sage.repl.load import load_wrap
 from sage.env import SAGE_IMPORTALL, SAGE_STARTUP_FILE
 from sage.misc.lazy_import import LazyImport
+from sage.misc.misc import run_once
 
 @magics_class
 class SageMagics(Magics):
@@ -583,41 +584,6 @@ def all_globals():
         return all_jupyter
 
 
-# from https://stackoverflow.com/questions/4103773/efficient-way-of-having-a-function-only-execute-once-in-a-loop
-from functools import wraps
-def run_once(func):
-    """
-    Runs a function (successfully) only once.
-
-    The running can be reset by setting the ``has_run`` attribute to False
-
-    TESTS::
-
-        sage: from sage.repl.ipython_extension import run_once
-        sage: @run_once
-        ....: def foo(work):
-        ....:     if work:
-        ....:         return 'foo worked'
-        ....:     raise RuntimeError("foo didn't work")
-        sage: foo(False)
-        Traceback (most recent call last):
-        ...
-        RuntimeError: foo didn't work
-        sage: foo(True)
-        'foo worked'
-        sage: foo(False)
-        sage: foo(True)
-    """
-    @wraps(func)
-    def wrapper(*args, **kwargs):
-        if not wrapper.has_run:
-            result = func(*args, **kwargs)
-            wrapper.has_run = True
-            return result
-    wrapper.has_run = False
-    return wrapper
-
-
 @run_once
 def load_ipython_extension(ip):
     """

src/sage/rings/qqbar.py

@@ -560,6 +560,7 @@
 from sage.misc.fast_methods import Singleton
 from sage.misc.cachefunc import cached_method
 from sage.misc.lazy_string import lazy_string
+from sage.misc.misc import increase_recursion_limit
 from sage.structure.coerce import parent_is_numerical, parent_is_real_numerical
 from sage.structure.sage_object import SageObject
 from sage.structure.richcmp import (richcmp, richcmp_method,
@@ -8543,9 +8544,7 @@ def exactify(self):
             sage: sys.setrecursionlimit(old_recursion_limit)
         """
         import sys
-        old_recursion_limit = sys.getrecursionlimit()
-        sys.setrecursionlimit(old_recursion_limit + 10)
-        try:
+        with increase_recursion_limit(10):
             left = self._left
             right = self._right
             left.exactify()
@@ -8560,8 +8559,7 @@ def exactify(self):
                 return ANRational(value)
             else:
                 return ANExtensionElement(gen, value)
-        finally:
-            sys.setrecursionlimit(old_recursion_limit)
+
 
 # These are the functions used to add, subtract, multiply, and divide
 # algebraic numbers. Basically, we try to compute exactly if both