import shelve
import threading

db = shelve.open("example.shelve")  # writeback=False by default
for i in range(100):
    db[str(i)] = i**2

def read_shelve(thread_id):
    for i in range(50):
        value = db[str(i)]
        print(f"Thread {thread_id} - {i}: {value}")

t1 = threading.Thread(target=read_shelve, args=(1,))
t2 = threading.Thread(target=read_shelve, args=(2,))
t1.start()
t2.start()
t1.join()
t2.join()

Exception in thread Thread-1 (read_shelve):
Exception in thread Thread-2 (read_shelve):
Traceback (most recent call last):
  File "/usr/lib/python3.13/shelve.py", line 111, in __getitem__
    value = self.cache[key]
            ~~~~~~~~~~^^^^^
KeyError: '0'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.13/dbm/sqlite3.py", line 79, in _execute
    return closing(self._cx.execute(*args, **kwargs))
                   ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
sqlite3.ProgrammingError: SQLite objects created in a thread can only be used in that same thread. The object was created in thread id 134486782028736 and this is thread id 134486754248384.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
Traceback (most recent call last):
  File "/usr/lib/python3.13/threading.py", line 1043, in _bootstrap_inner
    self.run()
    ~~~~~~~~^^
  File "/usr/lib/python3.13/shelve.py", line 111, in __getitem__
    value = self.cache[key]
            ~~~~~~~~~~^^^^^
  File "/usr/lib/python3.13/threading.py", line 994, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
KeyError: '0'
  File "/home/arf/test_shelve_multi/shelve_thread_shared_object.py", line 11, in read_shelve
    value = db[str(i)]
            ~~^^^^^^^^

During handling of the above exception, another exception occurred:

  File "/usr/lib/python3.13/shelve.py", line 113, in __getitem__
    f = BytesIO(self.dict[key.encode(self.keyencoding)])
                ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Traceback (most recent call last):
  File "/usr/lib/python3.13/dbm/sqlite3.py", line 89, in __getitem__
    with self._execute(LOOKUP_KEY, (key,)) as cu:
         ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.13/dbm/sqlite3.py", line 79, in _execute
    return closing(self._cx.execute(*args, **kwargs))
                   ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.13/dbm/sqlite3.py", line 81, in _execute
    raise error(str(exc))
sqlite3.ProgrammingError: SQLite objects created in a thread can only be used in that same thread. The object was created in thread id 134486782028736 and this is thread id 134486762641088.
dbm.sqlite3.error: SQLite objects created in a thread can only be used in that same thread. The object was created in thread id 134486782028736 and this is thread id 134486754248384.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.13/threading.py", line 1043, in _bootstrap_inner
    self.run()
    ~~~~~~~~^^
  File "/usr/lib/python3.13/threading.py", line 994, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/arf/test_shelve_multi/shelve_thread_shared_object.py", line 11, in read_shelve
    value = db[str(i)]
            ~~^^^^^^^^
  File "/usr/lib/python3.13/shelve.py", line 113, in __getitem__
    f = BytesIO(self.dict[key.encode(self.keyencoding)])
                ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.13/dbm/sqlite3.py", line 89, in __getitem__
    with self._execute(LOOKUP_KEY, (key,)) as cu:
         ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.13/dbm/sqlite3.py", line 81, in _execute
    raise error(str(exc))
dbm.sqlite3.error: SQLite objects created in a thread can only be used in that same thread. The object was created in thread id 134486782028736 and this is thread id 134486762641088.

import shelve
import threading

db = shelve.open("example.shelve", writeback=True)
for i in range(100):
    db[str(i)] = i**2


def read_shelve(thread_id):
    for i in range(50):
        value = db[str(i)]
        print(f"Thread {thread_id} - {i}: {value}")


t1 = threading.Thread(target=read_shelve, args=(1,))
t2 = threading.Thread(target=read_shelve, args=(2,))

t1.start()
t2.start()
t1.join()
t2.join()

import shelve
import threading

db = shelve.open("example.shelve", writeback=True)
for i in range(100):
    db[str(i)] = i**2


def read_shelve(thread_id):
    for i in range(50):
        value = db[str(i)]
        print(f"Thread {thread_id} - {i}: {value}")


t1 = threading.Thread(target=read_shelve, args=(1,))
t2 = threading.Thread(target=read_shelve, args=(2,))

t1.start()
t2.start()
t1.join()
t2.join()

import shelve
import threading

db = shelve.open("example.shelve")   # writeback=False by default
for i in range(100):
    db[str(i)] = i**2


def read_shelve(thread_id):
    for i in range(50):
        value = db[str(i)]
        print(f"Thread {thread_id} - {i}: {value}")


t1 = threading.Thread(target=read_shelve, args=(1,))
t2 = threading.Thread(target=read_shelve, args=(2,))

t1.start()
t2.start()
t1.join()
t2.join()