为什么要使用点“。”从setup.py安装`install

I am trying to use the method described here

Docker文件

FROM python:3.8

COPY requirements.txt setup.py /tmp/
RUN pip3 install -r /tmp/requirements.txt \
    && rm /tmp/*

这失败与：

Step 1/7 : FROM python:3.8
 ---> 79cc46abd78d
Step 2/7 : COPY requirements.txt setup.py /tmp/
 ---> Using cache
 ---> a50a0a8ecb06
Step 3/7 : RUN pip3 install -r /tmp/requirements.txt     && rm /tmp/*
 ---> Running in c7d29bd8f23c
ERROR: Directory '.' is not installable. Neither 'setup.py' nor 'pyproject.toml'
 found.

RUNpip3 install -r /tmp/requirements.txt

我不知道这里可能是什么问题。