[事故] pipが使えなくなった [とてもしょうもないメモ]

## 注意

とてもしょーもないです orz が、とてもくやしかったので記録として残しておきます。 orz orz orz

## 概要

pipが以下のようなエラーを吐いて動作しなくなってしまいました。

```
% pip3 install --user --upgrade django                                                                                                                                                                                                                                
Collecting django                                                                                                                                                                                                                                                                 
Exception:                                                                                                                                                                                                                                                                        
Traceback (most recent call last):                                                                                                                                                                                                                                                
  File "/home/rare/.local/lib/python3.6/site-packages/pip/basecommand.py", line 215, in main
    status = self.run(options, args)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/commands/install.py", line 335, in run
    wb.build(autobuilding=True)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/wheel.py", line 749, in build
    self.requirement_set.prepare_files(self.finder)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/req/req_set.py", line 380, in prepare_files
    ignore_dependencies=self.ignore_dependencies))
  File "/home/rare/.local/lib/python3.6/site-packages/pip/req/req_set.py", line 554, in _prepare_file
    require_hashes
  File "/home/rare/.local/lib/python3.6/site-packages/pip/req/req_install.py", line 278, in populate_link
    self.link = finder.find_requirement(self, upgrade)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/index.py", line 465, in find_requirement
    all_candidates = self.find_all_candidates(req.name)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/index.py", line 423, in find_all_candidates
    for page in self._get_pages(url_locations, project_name):
  File "/home/rare/.local/lib/python3.6/site-packages/pip/index.py", line 568, in _get_pages
    page = self._get_page(location)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/index.py", line 683, in _get_page
    return HTMLPage.get_page(link, session=self.session)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/index.py", line 792, in get_page
    "Cache-Control": "max-age=600",
  File "/home/rare/.local/lib/python3.6/site-packages/pip/_vendor/requests/sessions.py", line 488, in get
    return self.request('GET', url, **kwargs)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/download.py", line 386, in request
    return super(PipSession, self).request(method, url, *args, **kwargs)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/_vendor/requests/sessions.py", line 475, in request
    resp = self.send(prep, **send_kwargs)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/_vendor/requests/sessions.py", line 596, in send
    r = adapter.send(request, **kwargs)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/_vendor/cachecontrol/adapter.py", line 47, in send
    resp = super(CacheControlAdapter, self).send(request, **kw)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/_vendor/requests/adapters.py", line 423, in send
    timeout=timeout
  File "/home/rare/.local/lib/python3.6/site-packages/pip/_vendor/requests/packages/urllib3/connectionpool.py", line 589, in urlopen
    self._prepare_proxy(conn)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/_vendor/requests/packages/urllib3/connectionpool.py", line 797, in _prepare_proxy
    conn.connect()
  File "/home/rare/.local/lib/python3.6/site-packages/pip/_vendor/requests/packages/urllib3/connection.py", line 254, in connect
    conn = self._new_conn()
  File "/home/rare/.local/lib/python3.6/site-packages/pip/_vendor/requests/packages/urllib3/connection.py", line 142, in _new_conn
    (self.host, self.port), self.timeout, **extra_kw)
  File "/home/rare/.local/lib/python3.6/site-packages/pip/_vendor/requests/packages/urllib3/util/connection.py", line 66, in create_connection
    if host.startswith('['):
AttributeError: 'NoneType' object has no attribute 'startswith'
```

## 事故原因

```
% env | grep proxy
ftp_proxy=http://
http_proxy=http://
https_proxy=http://
```

## 原因の原因

```
% cat /etc/environment
ftp_proxy=http://
http_proxy=http://
https_proxy=http://
```

## まとめ

何故上記のような設定が紛れたのか、とんと検討つきません……。さようなら、私の2時間。
なお、pipに `--verbose` オプションつけたりとかで確認進めました。