使用 virtualenv/venv 和 pip 管理虚拟环境：
- 进入项目的根目录，创建虚拟环境：
virtualenv --python=python3 venv或python3 -m venv ./venv（venv不用安装，不过需要python3.3以上） - 进入虚拟环境：
source venv/bin/activate - 安装依赖：
pip install -r requirements.txt - 安装新包后，执行这个命令将包名和包版本信息写入 requirements.txt：
pip freeze > requirements.txt
| 资料 | 网址 |
|---|---|
| pypi：pi | https://pypi.org/project/pip/ |
命令：
pip freeze > requirements.txt # 安装包后，执行这个命令将包名和包版本信息写入requirements.txt
pip3 --help
pip --version # 看pip和pip3是不是同一个。
pip3 --version
pip3 list
$ pip3 --help
Usage:
pip3 <command> [options]
Commands:
install Install packages.
download Download packages.
uninstall Uninstall packages.
freeze Output installed packages in requirements format.
list List installed packages.
show Show information about installed packages.
check Verify installed packages have compatible dependencies.
config Manage local and global configuration.
search Search PyPI for packages.
wheel Build wheels from your requirements.
hash Compute hashes of package archives.
completion A helper command used for command completion.
help Show help for commands.
General Options:
-h, --help Show help.
--isolated Run pip in an isolated mode, ignoring environment variables and user configuration.
-v, --verbose Give more output. Option is additive, and can be used up to 3 times.
-V, --version Show version and exit.
-q, --quiet Give less output. Option is additive, and can be used up to 3 times (corresponding to WARNING, ERROR, and CRITICAL
logging levels).
--log <path> Path to a verbose appending log.
--proxy <proxy> Specify a proxy in the form [user:passwd@]proxy.server:port.
--retries <retries> Maximum number of retries each connection should attempt (default 5 times).
--timeout <sec> Set the socket timeout (default 15 seconds).
--exists-action <action> Default action when a path already exists: (s)witch, (i)gnore, (w)ipe, (b)ackup, (a)bort.
--trusted-host <hostname> Mark this host as trusted, even though it does not have valid or any HTTPS.
--cert <path> Path to alternate CA bundle.
--client-cert <path> Path to SSL client certificate, a single file containing the private key and the certificate in PEM format.
--cache-dir <dir> Store the cache data in <dir>.
--no-cache-dir Disable the cache.
--disable-pip-version-check
Don't periodically check PyPI to determine whether a new version of pip is available for download. Implied with
--no-index.
--no-color Suppress colored output