求助：Dockerfile 构建镜像，COPY 文件时返回错误：file does not exist [已解决]

Dockerfile 构建镜像，COPY 文件时返回如下错误：

......
......
Sending build context to Docker daemon  3.584kB
Step 1/13 : FROM python:3.9
 ---> 81f391f1a7d7
Step 2/13 : WORKDIR /app
 ---> Running in 478a4ae062bb
Removing intermediate container 478a4ae062bb
 ---> 355450ddba82
Step 3/13 : COPY requirements.txt /app/requirements.txt # 当前 dockerfile 为起始地址
COPY failed: file not found in build context or excluded by .dockerignore: stat app/requirements.txt: file does not exist
ERROR: Service 'python39' failed to build : Build failed

docker-compose 片段

python39:
    container_name: web_python39
    build:
      context: ./python/3.9 #
    networks:
      - hicrm_docker
    ports:
      - "50000:50000"
    restart: always
    tty: true
    volumes:
      - "${WEB_ROOT}/hidata:/app/hidata"
    command:
      - "/usr/local/bin/uwsgi --ini /www/hidata/serve/resources/uwsgi/uwsgu.dev.ini"

dockerfile 片段

FROM python:3.9

WORKDIR /app
COPY requirements.txt /app/ # 当前 dockerfile 为起始地址

ENV VIRTUAL_ENV=venv

RUN python3 -m venv venv
ENV PATH="$VIRTUAL_ENV/bin:$PATH"

RUN python3 -m pip install --upgrade pip
RUN pip install -r /app/requirements.txt
RUN pip install uwsgi
......

EXPOSE 50000

Dockerfile 文件和 requirements.txt 已放在在同一级目录

 /python/3.9/requirements.txt
 /python/3.9/Dockerfile