파이썬 ModuleNotFoundError: No module named '_cffi_backend'

pymysql을 새롭게 설치해 예제 코드를 실행했더니 이런 오류가 발생하는군요. ^^

Traceback (most recent call last):
  File "/home/testusr/.local/lib/python3.6/site-packages/uvicorn/protocols/http/h11_impl.py", line 373, in run_asgi
    result = await app(self.scope, self.receive, self.send)
  File "/home/testusr/.local/lib/python3.6/site-packages/uvicorn/middleware/proxy_headers.py", line 75, in __call__
    return await self.app(scope, receive, send)
  File "/home/testusr/.local/lib/python3.6/site-packages/fastapi/applications.py", line 269, in __call__
    await super().__call__(scope, receive, send)
  File "/home/testusr/.local/lib/python3.6/site-packages/starlette/applications.py", line 124, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/home/testusr/.local/lib/python3.6/site-packages/starlette/middleware/errors.py", line 184, in __call__
    raise exc
  File "/home/testusr/.local/lib/python3.6/site-packages/starlette/middleware/errors.py", line 162, in __call__
    await self.app(scope, receive, _send)
  File "/home/testusr/.local/lib/python3.6/site-packages/starlette/middleware/base.py", line 68, in __call__
    response = await self.dispatch_func(request, call_next)
  File "/mnt/d/workshop2/python-agent/jennifer/wrap/middleware_fastapi.py", line 121, in dispatch
    raise err
  File "/mnt/d/workshop2/python-agent/jennifer/wrap/middleware_fastapi.py", line 97, in dispatch
    response = await call_next(request)
  File "/home/testusr/.local/lib/python3.6/site-packages/starlette/middleware/base.py", line 46, in call_next
    raise app_exc
  File "/home/testusr/.local/lib/python3.6/site-packages/starlette/middleware/base.py", line 36, in coro
    await self.app(scope, request.receive, send_stream.send)
  File "/home/testusr/.local/lib/python3.6/site-packages/starlette/exceptions.py", line 93, in __call__
    raise exc
  File "/home/testusr/.local/lib/python3.6/site-packages/starlette/exceptions.py", line 82, in __call__
    await self.app(scope, receive, sender)
  File "/home/testusr/.local/lib/python3.6/site-packages/fastapi/middleware/asyncexitstack.py", line 21, in __call__
    raise e
  File "/home/testusr/.local/lib/python3.6/site-packages/fastapi/middleware/asyncexitstack.py", line 18, in __call__
    await self.app(scope, receive, send)
  File "/home/testusr/.local/lib/python3.6/site-packages/starlette/routing.py", line 670, in __call__
    await route.handle(scope, receive, send)
  File "/home/testusr/.local/lib/python3.6/site-packages/starlette/routing.py", line 266, in handle
    await self.app(scope, receive, send)
  File "/home/testusr/.local/lib/python3.6/site-packages/starlette/routing.py", line 65, in app
    response = await func(request)
  File "/home/testusr/.local/lib/python3.6/site-packages/fastapi/routing.py", line 232, in app
    dependant=dependant, values=values, is_coroutine=is_coroutine
  File "/home/testusr/.local/lib/python3.6/site-packages/fastapi/routing.py", line 160, in run_endpoint_function
    return await dependant.call(**values)
  File "./main.py", line 274, in mysql_test
    text3 = test_pymysql_1()
  File "./main.py", line 512, in test_pymysql_1
    con = pymysql.connect(host=mysql_ip, user="...", password="...", database="...", charset='utf8')
  File "/mnt/d/testapp/test.py", line 354, in handler
    raise e
  File "/mnt/d/testapp/test.py", line 344, in handler
    origin_connection = connect(*args, **kwargs)
  File "/home/testusr/.local/lib/python3.6/site-packages/pymysql/connections.py", line 353, in __init__
    self.connect()
  File "/home/testusr/.local/lib/python3.6/site-packages/pymysql/connections.py", line 633, in connect
    self._request_authentication()
  File "/home/testusr/.local/lib/python3.6/site-packages/pymysql/connections.py", line 921, in _request_authentication
    auth_packet = self._process_auth(plugin_name, auth_packet)
  File "/home/testusr/.local/lib/python3.6/site-packages/pymysql/connections.py", line 957, in _process_auth
    return _auth.caching_sha2_password_auth(self, auth_packet)
  File "/home/testusr/.local/lib/python3.6/site-packages/pymysql/_auth.py", line 265, in caching_sha2_password_auth
    data = sha2_rsa_encrypt(conn.password, conn.salt, conn.server_public_key)
  File "/home/testusr/.local/lib/python3.6/site-packages/pymysql/_auth.py", line 147, in sha2_rsa_encrypt
    rsa_key = serialization.load_pem_public_key(public_key, default_backend())
  File "/usr/lib/python3/dist-packages/cryptography/hazmat/backends/__init__.py", line 15, in default_backend
    from cryptography.hazmat.backends.openssl.backend import backend
  File "/usr/lib/python3/dist-packages/cryptography/hazmat/backends/openssl/__init__.py", line 7, in <module>
    from cryptography.hazmat.backends.openssl.backend import backend
  File "/usr/lib/python3/dist-packages/cryptography/hazmat/backends/openssl/backend.py", line 16, in <module>
    from cryptography import utils, x509
  File "/usr/lib/python3/dist-packages/cryptography/x509/__init__.py", line 8, in <module>
    from cryptography.x509.base import (
  File "/usr/lib/python3/dist-packages/cryptography/x509/base.py", line 18, in <module>
    from cryptography.x509.extensions import Extension, ExtensionType
  File "/usr/lib/python3/dist-packages/cryptography/x509/extensions.py", line 20, in <module>
    from cryptography.hazmat.primitives import constant_time, serialization
  File "/usr/lib/python3/dist-packages/cryptography/hazmat/primitives/constant_time.py", line 11, in <module>
    from cryptography.hazmat.bindings._constant_time import lib
ModuleNotFoundError: No module named '_cffi_backend'

python3 -m pip install cffi