confusing error for bad timeout value

Calling requests.get(...., timeout=X) with a bad value for X causes urllib3 to throw an exception.

If X is a tuple, then requests raises its own exception too (good!).

If not, then requests doesn't say that it got a bad timeout value.

#5017 suggested a fix, but was closed

Expected Result

These two lines should both raise an exception in requests:

get("https://random.org", timeout=(True, True))
get("https://random.org", timeout=True) 

Actual Result

The first line outputs:

Traceback (most recent call last):
  File "..../requests/adapters.py", line 425, in send
    timeout = TimeoutSauce(connect=connect, read=read)
  File "..../urllib3/util/timeout.py", line 94, in __init__
    self._connect = self._validate_timeout(connect, 'connect')
  File "..../urllib3/util/timeout.py", line 121, in _validate_timeout
    raise ValueError("Timeout cannot be a boolean value. It must "
ValueError: Timeout cannot be a boolean value. It must be an int, float or None.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "test.py", line 3, in <module>
    get("https://random.org", timeout=(True, True))
  File "..../requests/api.py", line 76, in get
    return request('get', url, params=params, **kwargs)
  File "..../requests/api.py", line 61, in request
    return session.request(method=method, url=url, **kwargs)
  File "..../requests/sessions.py", line 537, in request
    resp = self.send(prep, **send_kwargs)
  File "..../requests/sessions.py", line 650, in send
    r = adapter.send(request, **kwargs)
  File "..../requests/adapters.py", line 431, in send
    raise ValueError(err)
ValueError: Invalid timeout (True, True). Pass a (connect, read) timeout tuple, or a single float to set both timeouts to the same value

The second outputs:

Traceback (most recent call last):
  File "test.py", line 3, in <module>
    get("https://random.org", timeout=True)
  File "..../requests/api.py", line 76, in get
    return request('get', url, params=params, **kwargs)
  File "..../requests/api.py", line 61, in request
    return session.request(method=method, url=url, **kwargs)
  File "..../requests/sessions.py", line 537, in request
    resp = self.send(prep, **send_kwargs)
  File "..../requests/sessions.py", line 650, in send
    r = adapter.send(request, **kwargs)
  File "..../requests/adapters.py", line 435, in send
    timeout = TimeoutSauce(connect=timeout, read=timeout)
  File "..../urllib3/util/timeout.py", line 94, in __init__
    self._connect = self._validate_timeout(connect, 'connect')
  File "..../urllib3/util/timeout.py", line 121, in _validate_timeout
    raise ValueError("Timeout cannot be a boolean value. It must "
ValueError: Timeout cannot be a boolean value. It must be an int, float or None.

Reproduction Steps

import requests
get("https://random.org", timeout=True) 

System Information

$ python -m requests.help

{
  "chardet": {
    "version": "3.0.4"
  },
  "cryptography": {
    "version": "1.3.2"
  },
  "idna": {
    "version": "2.6"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.5.1"
  },
  "platform": {
    "release": "15.0.0",
    "system": "Darwin"
  },
  "pyOpenSSL": {
    "openssl_version": "1000208f",
    "version": "16.0.0"
  },
  "requests": {
    "version": "2.22.0"
  },
  "system_ssl": {
    "version": "1000212f"
  },
  "urllib3": {
    "version": "1.22"
  },
  "using_pyopenssl": true
}

Start in requests/adapters.py, following the timeout handling shown in the traceback, and review the related request path in sessions.py. Reproduce the two timeout calls and add regression coverage so both invalid values raise the intended requests error rather than exposing urllib3 validation directly.