python3.8 use async getting invalid sysntax

 File "/data/yangjun/fact/wikifact/scripts/search_module.py", line 2, in <module>                                                                           from drqa.retriever import DocDB, utils                                                                                                                   File "/data/yangjun/.conda/envs/tor18/lib/python3.8/site-packages/drqa/__init__.py", line 20, in <module>                                                     from . import tokenizersFile "/data/yangjun/.conda/envs/tor18/lib/python3.8/site-packages/drqa/tokenizers/__init__.py", line 20, in <module>from .corenlp_tokenizer import CoreNLPTokenizerFile "/data/yangjun/.conda/envs/tor18/lib/python3.8/site-packages/drqa/tokenizers/corenlp_tokenizer.py", line 14, in <module>import pexpectFile "/data/yangjun/.conda/envs/tor18/lib/python3.8/site-packages/pexpect/__init__.py", line 75, in <module>from .pty_spawn import spawn, spawnuFile "/data/yangjun/.conda/envs/tor18/lib/python3.8/site-packages/pexpect/pty_spawn.py", line 14, in <module>from .spawnbase import SpawnBaseFile "/data/yangjun/.conda/envs/tor18/lib/python3.8/site-packages/pexpect/spawnbase.py", line 224                                                             def expect(self, pattern, timeout=-1, searchwindowsize=-1, async=False):                                                                                                                                               ^                                                                                            SyntaxError: invalid syntax

解决方案：

python -m pip install --upgrade pip
python -m pip install pexpect --upgrade