我试图在Flask_App所在的Downloads目录中执行'flask run'。我的Flask_App是'applications.py'。当我在开发环境中执行'flask run'时，我会得到一个URL。一旦我将URL粘贴到Safari，我就会得到这个错误。

ImportError: dlopen(/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/psycopg2/_psycopg.cpython-37m-darwin.so, 2): Symbol not found: _PQencryptPasswordConn
  Referenced from: /Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/psycopg2/_psycopg.cpython-37m-darwin.so
  Expected in: /usr/lib/libpq.5.6.dylib
 in /Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/psycopg2/_psycopg.cpython-37m-darwin.so

我用的是MacOSX High Sierra。我的PostgreSQL版本是11。我的Python更新到3.7版本了。pip升级了，psycopg也升级到了2.8.3版本。我尝试在不同的目录下运行'flask run'，并尝试将'applications.py'移动到我当前所在的不同库和目录中。我试过使用sudo，但我意识到我不知道密码。在过去，当我不小心删除了我的管理员帐户的管理员状态时，我强制创建了另一个管理员帐户...不知道这是否影响了sudo，但它不接受我当前的管理员密码。我在安装psycopg 2时也遇到了问题，但通过重新下载PostgreSQL 11解决了这个问题。我已经使用pip成功安装了SQLAlchemy和Flask-Session。
我试着注解掉代码中的几行，并将其缩小到'create_engine'函数，因为只需'os.getenv（“DATABASE_URL”）'就可以按预期运行我的页面。
这是我的'applications.py'代码

import os

from flask import Flask, session
from flask_session import Session
from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session, sessionmaker

app = Flask(__name__)

# Check for environment variable
if not os.getenv("DATABASE_URL"):
    raise RuntimeError("DATABASE_URL is not set")

# Configure session to use filesystem
app.config["SESSION_PERMANENT"] = False
app.config["SESSION_TYPE"] = "filesystem"
Session(app)

# Set up database
engine = create_engine(os.getenv("DATABASE_URL"))
db = scoped_session(sessionmaker(bind=engine))

@app.route("/")
def index():
    return "Project 1: TODO"

一旦我粘贴了URL，我期望页面显示文本“项目1：TODO”然而，相反，我得到这个错误消息：

flask.cli.NoAppException: While importing "applications", an ImportError was raised:

Traceback (most recent call last):
  File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/flask/cli.py", line 235, in locate_app
    __import__(module_name)
  File "/Users/dhruvaiyer/Downloads/applications.py", line 20, in <module>
    engine = create_engine(os.getenv("DATABASE_URL"))
  File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/sqlalchemy/engine/__init__.py", line 425, in create_engine
    return strategy.create(*args, **kwargs)
  File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/sqlalchemy/engine/strategies.py", line 81, in create
    dbapi = dialect_cls.dbapi(**dbapi_args)
  File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/sqlalchemy/dialects/postgresql/psycopg2.py", line 584, in dbapi
    import psycopg2
  File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/psycopg2/__init__.py", line 50, in <module>
    from psycopg2._psycopg import (                     # noqa
ImportError: dlopen(/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/psycopg2/_psycopg.cpython-37m-darwin.so, 2): Symbol not found: _PQencryptPasswordConn
  Referenced from: /Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/psycopg2/_psycopg.cpython-37m-darwin.so
  Expected in: /usr/lib/libpq.5.6.dylib
 in /Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/psycopg2/_psycopg.cpython-37m-darwin.so

File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/flask/cli.py", line 325, in __call__
self._flush_bg_loading_exception()
File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/flask/cli.py", line 313, in _flush_bg_loading_exception
reraise(*exc_info)
File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/flask/_compat.py", line 35, in reraise
raise value
File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/flask/cli.py", line 302, in _load_app
self._load_unlocked()
File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/flask/cli.py", line 317, in _load_unlocked
self._app = rv = self.loader()
File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/flask/cli.py", line 372, in load_app
app = locate_app(self, import_name, name)
File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/flask/cli.py", line 242, in locate_app
'\n\n{tb}'.format(name=module_name, tb=traceback.format_exc())
flask.cli.NoAppException: While importing "applications", an ImportError was raised: Traceback (most recent call last): File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/flask/cli.py", line 235, in locate_app __import__(module_name) File "/Users/dhruvaiyer/Downloads/applications.py", line 20, in <module> engine = create_engine(os.getenv("DATABASE_URL")) File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/sqlalchemy/engine/__init__.py", line 425, in create_engine return strategy.create(*args, **kwargs) File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/sqlalchemy/engine/strategies.py", line 81, in create dbapi = dialect_cls.dbapi(**dbapi_args) File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/sqlalchemy/dialects/postgresql/psycopg2.py", line 584, in dbapi import psycopg2 File "/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/psycopg2/__init__.py", line 50, in <module> from psycopg2._psycopg import ( # noqa ImportError: dlopen(/Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/psycopg2/_psycopg.cpython-37m-darwin.so, 2): Symbol not found: _PQencryptPasswordConn Referenced from: /Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/psycopg2/_psycopg.cpython-37m-darwin.so Expected in: /usr/lib/libpq.5.6.dylib in /Users/dhruvaiyer/anaconda3/lib/python3.7/site-packages/psycopg2/_psycopg.cpython-37m-darwin.so
#The debugger caught an exception in your WSGI application. You can now look at the traceback which led to the error.

同样的代码也出现在我的终端窗口中。对于如何进行或如何解决这个问题有什么建议吗？非常感谢你提前！