No module named 'flask'`

为什么会提示没有flask呢
```
web_1 | pdm.exceptions.PdmUsageError: Unsupported shell: sh, please specify another shell via `--pep582 `
web_1 | Traceback (most recent call last):
web_1 | File "/app/__pypackages__/3.9/bin/flask", line 5, in
web_1 | from flask.cli import main
web_1 | ModuleNotFoundError: No module named 'flask'
web_1 | Traceback (most recent call last):
web_1 | File "/usr/local/bin/pdm", line 8, in
web_1 | sys.exit(main())
web_1 | File "/usr/local/lib/python3.9/site-packages/pdm/core.py", line 219, in main
web_1 | return Core().main(args)
web_1 | File "/usr/local/lib/python3.9/site-packages/pdm/core.py", line 143, in main
web_1 | print_pep582_command(self.ui, options.pep582)
web_1 | File "/usr/local/lib/python3.9/site-packages/pdm/cli/actions.py", line 712, in print_pep582_command
web_1 | raise PdmUsageError(
web_1 | pdm.exceptions.PdmUsageError: Unsupported shell: sh, please specify another shell via `--pep582 `
web_1 | Traceback (most recent call last):
web_1 | File "/app/__pypackages__/3.9/bin/flask", line 5, in
web_1 | from flask.cli import main
web_1 | ModuleNotFoundError: No module named 'flask'
```