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Python

Python 是一个非常适合数学计算的语言，因为它非常好写，而且有了 numpy 和 matplotlib 这两个库文件，Python 可以在许多情况下代替 Matlab 这样昂贵的(至少在中国很昂贵)商业软件。

虚拟环境

Section titled “虚拟环境”

Python 提供了一个包管理器 pip，在 Windows 上它运行良好，但是在 Debian/Ubuntu 上默认禁止使用 pip 来安装库文件。

Terminal window
error: externally-managed-environment


× This environment is externally managed
╰─> To install Python packages system-wide, try apt install
    python3-xyz, where xyz is the package you are trying to
    install.


    If you wish to install a non-Debian-packaged Python package,
    create a virtual environment using python3 -m venv path/to/venv.
    Then use path/to/venv/bin/python and path/to/venv/bin/pip. Make
    sure you have python3-full installed.


    If you wish to install a non-Debian packaged Python application,
    it may be easiest to use pipx install xyz, which will manage a
    virtual environment for you. Make sure you have pipx installed.


    See /usr/share/doc/python3.11/README.venv for more information.


note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.

这个报错看起来有点唬人，因为后面有个 —break-system-packages 推荐的解决方法是

Terminal window
python3 -m venv venv    # 创建 | python3.12 -m venv venv
source venv/bin/active  # 启用
deactive                # 退出

显然 venv/bin 目录下的 active 是一个脚本，可以查看到它的内容如下

Terminal window
# This file must be used with "source bin/activate" *from bash*
# You cannot run it directly


deactivate () {
    # reset old environment variables
    if [ -n "${_OLD_VIRTUAL_PATH:-}" ] ; then
        PATH="${_OLD_VIRTUAL_PATH:-}"
        export PATH
        unset _OLD_VIRTUAL_PATH
    fi
    if [ -n "${_OLD_VIRTUAL_PYTHONHOME:-}" ] ; then
        PYTHONHOME="${_OLD_VIRTUAL_PYTHONHOME:-}"
        export PYTHONHOME
        unset _OLD_VIRTUAL_PYTHONHOME
    fi


    # Call hash to forget past locations. Without forgetting
    # past locations the $PATH changes we made may not be respected.
    # See "man bash" for more details. hash is usually a builtin of your shell
    hash -r 2> /dev/null


    if [ -n "${_OLD_VIRTUAL_PS1:-}" ] ; then
        PS1="${_OLD_VIRTUAL_PS1:-}"
        export PS1
        unset _OLD_VIRTUAL_PS1
    fi


    unset VIRTUAL_ENV
    unset VIRTUAL_ENV_PROMPT
    if [ ! "${1:-}" = "nondestructive" ] ; then
    # Self destruct!
        unset -f deactivate
    fi
}


# unset irrelevant variables
deactivate nondestructive


# on Windows, a path can contain colons and backslashes and has to be converted:
case "$(uname)" in
    CYGWIN*|MSYS*|MINGW*)
        # transform D:\path\to\venv to /d/path/to/venv on MSYS and MINGW
        # and to /cygdrive/d/path/to/venv on Cygwin
        VIRTUAL_ENV=$(cygpath /workspace/Docs/Docs/venv)
        export VIRTUAL_ENV
        ;;
    *)
        # use the path as-is
        export VIRTUAL_ENV=/workspace/Docs/Docs/venv
        ;;
esac


_OLD_VIRTUAL_PATH="$PATH"
PATH="$VIRTUAL_ENV/"bin":$PATH"
export PATH


VIRTUAL_ENV_PROMPT=venv
export VIRTUAL_ENV_PROMPT


# unset PYTHONHOME if set
# this will fail if PYTHONHOME is set to the empty string (which is bad anyway)
# could use `if (set -u; : $PYTHONHOME) ;` in bash
if [ -n "${PYTHONHOME:-}" ] ; then
    _OLD_VIRTUAL_PYTHONHOME="${PYTHONHOME:-}"
    unset PYTHONHOME
fi


if [ -z "${VIRTUAL_ENV_DISABLE_PROMPT:-}" ] ; then
    _OLD_VIRTUAL_PS1="${PS1:-}"
    PS1="("venv") ${PS1:-}"
    export PS1
fi


# Call hash to forget past commands. Without forgetting
# past commands the $PATH changes we made may not be respected
hash -r 2> /dev/null

这个脚本主要是将虚拟环境的路径添加到了环境变量中，同时用 _OLD_VIRTUAL_PATH 缓存了旧的环境变量以确保可以用 deactive 命令还原。最后在命令行的开头添加了 (venv) 以做提醒。于是现在可以自由的使用 pip，下载的所有文件都会保存到 venv 路径中不会对系统造成任何影响。

Module

Section titled “Module”
Terminal window
python3 -h
usage: python3 [option] ... [-c cmd | -m mod | file | -] [arg] ...
Options (and corresponding environment variables):
--------------- a lot of args -----------------------------------
-m mod : run library module as a script (terminates option list)
--------------- a lot of args -----------------------------------

按照 python3 -h 的输出结果来看，-m 参数可以以一个脚本的形式执行 Python 库中的一个模型。其中比较有用的有

http.server

Section titled “http.server”
Terminal window
python3 -m http.server

这样会直接监听 0.0.0.0:8000 端口，对于如下目录结构，在浏览器中访问该地址就会看到

  • Directorysrc
    • example.jpg
    • main.py
    • README.md

code-python-1

uploadserver

Section titled “uploadserver”
Terminal window
pip install uploadserver
python -m uploadserver

这是一个需要单独下载的模块，多了一个上传文件的按钮。

公网访问

Section titled “公网访问”

需要一个公网 IPv4 或者 IPv6 地址。公网 IPv4 一般只在云服务器上出现，但是 IPv6 就到处都是了。

Terminal window
python3 -m http.server -b ::

IPv6 过长，大多数情况下会用 :: 来表示地址中连续的 0 。上面的 :: 即为

Terminal window
0000:0000:0000:0000:0000:0000:0000:0000

所以会产生以下两种不同的输出

Terminal window
Serving HTTP on :: port 8000 (http://[::]:8000/) ...
Serving HTTP on 0.0.0.0 port 8000 (http://0.0.0.0:8000/) ...

关于内网穿透，这个会在 Cloud 章节中介绍。绝大多数情况下，IPv6 都是最好的选择。无论你以何种方式传输文件，最终的速度都不会超过中国运营商的硬性限速，大约 30~50Mbps