Use context manager to open files

[RichieB2B]

In the documentation for POST a Multipart-Encoded File the example code opens the file inline but never closes it. This leaves the file open until the script ends. It is better to use a context manager even in example code.

Original:

>>> url = 'https://httpbin.org/post'
>>> files = {'file': open('report.xls', 'rb')}

>>> r = requests.post(url, files=files)
>>> r.text

Replace with:

>>> url = 'https://httpbin.org/post'
>>> with open('report.xls', 'rb') as fd:
...     files = {'file': fd}

...     r = requests.post(url, files=files)
...     r.text

[lpaladin]

I've just got bitten by this example, and was just about to create a PR for this too 😃

(Maybe

    ...     r = requests.post(url, files=multiple_files)
    ...     r.text

could be

    ...     r = requests.post(url, files=multiple_files)
    ... 
    >>> r.text