0. Emacs + LSP
python-language-server 是 LSP 的 Python 实现。
本文介绍了 Emacs lsp-mode 与 python-language-server 一起使用的办法。
1. emacs lsp-mode
1.1 安装emacs
本例中使用的是，Emacs For Mac OS X，下载后安装即可。
1.2 .emacs.d配置
emacs启动时默认执行 ~/.emacs.d/init.el，我们新建一个 init.el，写入如下内容，
配置 emacs 从 melpha 下载 package。
(require 'package)
(let* ((no-ssl (and (memq system-type '(windows-nt ms-dos))
(not (gnutls-available-p))))
(proto (if no-ssl "http" "https")))
(when no-ssl
(warn "\
Your version of Emacs does not support SSL connections,
which is unsafe because it allows man-in-the-middle attacks.
There are two things you can do about this warning:
1. Install an Emacs version that does support SSL and be safe.
2. Remove this warning from your init file so you won't see it again."))
;; Comment/uncomment these two lines to enable/disable MELPA and MELPA Stable as desired
(add-to-list 'package-archives (cons "melpa" (concat proto "://melpa.org/packages/")) t)
;;(add-to-list 'package-archives (cons "melpa-stable" (concat proto "://stable.melpa.org/packages/")) t)
(when (< emacs-major-version 24)
;; For important compatibility libraries like cl-lib
(add-to-list 'package-archives (cons "gnu" (concat proto "://elpa.gnu.org/packages/")))))
(package-initialize)
1.3 安装package
打开emacs，先更新package列表，然后安装use-package，python-mode 和 lsp-mode。
（1）更新package列表
M-x package-refresh-contents <RET>
表示先按Alt + x，然后输入 package-refresh-contents，最后按 回车。
（2）安装package
M-x package-install <RET> use-package <RET>
M-x package-install <RET> python-mode <RET>
M-x package-install <RET> lsp-mode <RET>
M-x package-install <RET> company-lsp <RET>
安装完后，发现 ~/.emacs.d/init.el 中多了以下内容，
(custom-set-variables
;; custom-set-variables was added by Custom.
;; If you edit it by hand, you could mess it up, so be careful.
;; Your init file should contain only one such instance.
;; If there is more than one, they won't work right.
'(package-selected-packages (quote (lsp-mode python-mode use-package))))
(custom-set-faces
;; custom-set-faces was added by Custom.
;; If you edit it by hand, you could mess it up, so be careful.
;; Your init file should contain only one such instance.
;; If there is more than one, they won't work right.
)
1.4 启用lsp-mode
打开 ~/.emacs.d/init.el，加入如下内容，
(setq lsp-clients-python-command "/usr/local/bin/pyls")
(use-package lsp-mode
:hook (python-mode . lsp)
:commands lsp)
其中，lsp-clients-python-command 要设置为 python-language-server 可执行文件的地址（下文介绍），emacs 会自动启动 server。
:hook (python-mode . lsp) 表示启用 python-mode 时调用命令 lsp。
2. python-language-server
2.1 正常安装
$ pip install -U setuptools
$ pip install 'python-language-server[all]'
python-language-server的安装路径为，/Library/Python/2.7/site-packages，
$ pip show python-language-server
Name: python-language-server
Version: 0.26.1
Summary: Python Language Server for the Language Server Protocol
Home-page: https://github.com/palantir/python-language-server
Author: Palantir Technologies, Inc.
Author-email: None
License: UNKNOWN
Location: /Library/Python/2.7/site-packages
Requires: future, configparser, pluggy, jedi, futures, backports.functools-lru-cache, python-jsonrpc-server
Required-by: pyls-isort
可执行文件 pyls 位于 /usr/local/bin/pyls
$ which pyls
/usr/local/bin/pyls
2.2 可能的一些错误
安装过程中，可能会遇到一系列的报错。
（1）安装 pip 时 sudo easyinstall pip 报错
Could not find suitable distribution for Requirement.parse('pip')
解决方案：
$ curl 'https://bootstrap.pypa.io/get-pip.py' > get-pip.py
$ sudo python get-pip.py
$ sudo easy_install pip
参考：https://segmentfault.com/q/1010000014299471
（2）pip install 'python-language-server[all]' 报错
'install_requires' must be a string or list of strings
解决方案：
# install python
$ brew install python2
# change the path of the current terminal session
$ export PATH=/usr/local/share/python:$PATH
# setup the brew-installed pip
$ sudo pip install -U setuptools
# finally, install pls
$ sudo pip install 'python-language-server[all]'
参考：https://github.com/palantir/python-language-server/issues/349
（3）pip install --upgrade setuptools 报错
Could not install packages due to an EnvironmentError
解决方案：
$ sudo pip install setuptools --upgrade --ignore-installed
参考：https://github.com/pypa/pip/issues/5329
（4）setuptools_scm 报错
"setuptools_scm" could not be found
解决方案：
$ sudo pip install setuptools_scm
参考：https://github.com/pypa/pypi-legacy/issues/322
3. main.py
3.1 select action
新建一个 main.py 文件，用emacs打开，
消息区会显示：
main.py is not part of any project. Select aciton:
这里要按 <Tab> 键，进行选择，
选最后一个就好，
Import project root /Users/xxx/.../
其中，Yasnippet is not present but ‘lsp-enable-snippet’ is set to ‘t’，
可以在 ~/.emacs.d/init.el 中加入如下配置解决，
(setq lsp-enable-snippet nil)
3.2 LSP Connection
选好 action 后，emacs 会自动启动 pyls，并建立连接，
消息区显示，
LSP :: Connected to [pyls:3578 status:starting]
3.3 智能提示
我们在编辑区输入 print，emacs弹出了智能提示，
注：这个提示是 company-lsp 弹出的。
