AttributeError: module 'os' has no attribute 'link'. Did you mean: 'unlink'?

[vzool]

BUG

What I did:

import ZODB # just import & run

What I expect to happen:

Run without errors

What actually happened:

Traceback (most recent call last):
  File "/data/user/0/ru.iiec.pydroid3/files/accomp_files/iiec_run/iiec_run.py", line 31, in <module>
    start(fakepyfile,mainpyfile)
  File "/data/user/0/ru.iiec.pydroid3/files/accomp_files/iiec_run/iiec_run.py", line 30, in start
    exec(open(mainpyfile).read(),  __main__.__dict__)
  File "<string>", line 15, in <module>
  File "/data/user/0/ru.iiec.pydroid3/files/aarch64-linux-android/lib/python3.11/site-packages/ZODB/__init__.py", line 21, in <module>
    from ZODB.DB import DB
  File "/data/user/0/ru.iiec.pydroid3/files/aarch64-linux-android/lib/python3.11/site-packages/ZODB/DB.py", line 33, in <module>
    from ZODB.Connection import Connection
  File "/data/user/0/ru.iiec.pydroid3/files/aarch64-linux-android/lib/python3.11/site-packages/ZODB/Connection.py", line 35, in <module>
    from ZODB.blob import SAVEPOINT_SUFFIX
  File "/data/user/0/ru.iiec.pydroid3/files/aarch64-linux-android/lib/python3.11/site-packages/ZODB/blob.py", line 950, in <module>
    link_or_copy = os.link
                   ^^^^^^^
AttributeError: module 'os' has no attribute 'link'. Did you mean: 'unlink'?

[Program finished]

What version of Python and Zope/Addons I am using:

Python: 3.11.4
Zope/Addons: None
Platform: Android 13 Arm64
Application: Pydroid 3

[icemac]

Android 13 is not officially supported by ZODB.

Are you sure you have a complete Python installation on your device?
According to https://docs.python.org/3/library/os.html#os.link os.link should exist on any Unix or Windows.

The failing code is in

ZODB/src/ZODB/blob.py

Lines 931 to 950 in 783610f

	if sys.platform == 'win32':
	# On Windows, you can't remove read-only files, so make the
	# file writable first.
	def remove_committed(filename):
	os.chmod(filename, stat.S_IWRITE)
	os.remove(filename)
	def remove_committed_dir(path):
	for (dirpath, dirnames, filenames) in os.walk(path):
	for filename in filenames:
	filename = os.path.join(dirpath, filename)
	remove_committed(filename)
	shutil.rmtree(path)
	link_or_copy = shutil.copy
	else:
	remove_committed = os.remove
	remove_committed_dir = shutil.rmtree
	link_or_copy = os.link

Here different options are set for different OS.
To be successfull you need either os.link or at least shutil.copy, so try to modify the code to use the latter one and report back your findings.

[vzool]

According to this solution pyodide/pyodide#3880 (comment), I could resolve the issue by the following hack:

# --- <hack>
import os
print(hasattr(os, 'link')) # --> False
os.link = os.symlink
print(hasattr(os, 'link')) # --> True
# --- </hack>
import ZODB # just import & run
# imported successfully

[vzool]

I just hit another error:

False
True
Traceback (most recent call last):
  File "/data/user/0/ru.iiec.pydroid3/files/aarch64-linux-android/lib/python3.11/site-packages/zc/lockfile/__init__.py", line 60, in _lock_file
    fcntl.flock(file.fileno(), _flags)
OSError: [Errno 38] Function not implemented

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/data/user/0/ru.iiec.pydroid3/files/accomp_files/iiec_run/iiec_run.py", line 31, in <module>
    start(fakepyfile,mainpyfile)
  File "/data/user/0/ru.iiec.pydroid3/files/accomp_files/iiec_run/iiec_run.py", line 30, in start
    exec(open(mainpyfile).read(),  __main__.__dict__)
  File "<string>", line 25, in <module>
  File "/data/user/0/ru.iiec.pydroid3/files/aarch64-linux-android/lib/python3.11/site-packages/ZODB/FileStorage/FileStorage.py", line 251, in __init__
    self._lock_file = LockFile(file_name + '.lock')
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/data/user/0/ru.iiec.pydroid3/files/aarch64-linux-android/lib/python3.11/site-packages/zc/lockfile/__init__.py", line 120, in __init__
    super().__init__(path)
  File "/data/user/0/ru.iiec.pydroid3/files/aarch64-linux-android/lib/python3.11/site-packages/zc/lockfile/__init__.py", line 93, in __init__
    _lock_file(fp)
  File "/data/user/0/ru.iiec.pydroid3/files/aarch64-linux-android/lib/python3.11/site-packages/zc/lockfile/__init__.py", line 62, in _lock_file
    raise LockError("Couldn't lock %r" % file.name)
zc.lockfile.LockError: Couldn't lock 'mydata.fs.lock'

[Program finished]

The Code

import persistent

class Account(persistent.Persistent):

    def __init__(self):
        self.balance = 0.0

    def deposit(self, amount):
        self.balance += amount

    def cash(self, amount):
        assert amount < self.balance
        self.balance -= amount
 
# --- <hack>
import os
print(hasattr(os, 'link')) # --> False
os.link = os.symlink
print(hasattr(os, 'link')) # --> True
# --- </hack>
import ZODB # just import & run
# imported successfully

import ZODB.FileStorage
storage = ZODB.FileStorage.FileStorage('mydata.fs')
db = ZODB.DB(storage)
connection = db.open()
root = connection.root

import BTrees._OOBTree
root.accounts = BTrees.OOBTree.BTree()
root.accounts['account-1'] = Account()
root.accounts['account-1'].deposit(9630)

import transaction
transaction.commit()

[icemac]

Your Python is also not implementing fcntl.flock, even though the fcntl module is there. Here https://github.com/zopefoundation/zc.lockfile/blob/4c2c7b50ea8ae54d8bb39e164f50343d00d41d30/src/zc/lockfile/__init__.py#L27 zc.lockfile expects that you have a working flock function if you have fcntl.