Pass multiple values of headers using list or tuple

[GeekDuanLian]

For example, the Accept header may have multiple values.
Can pass multiple values like this:
s.get('xxx', headers={'Accept': ['text/html', 'application/json']})
Which is equivalent to:
s.get('xxx', headers={'Accept': 'text/html, application/json'})
But more pythonic.

[tomchristie]

I'm probably in favour of this, yes.

There are a few cases which shouldn't concatenate, but should instead result in multiple headers. Eg... https://github.com/bnoordhuis/mozilla-central/blob/master/netwerk/protocol/http/nsHttpHeaderArray.h#L185

[GeekDuanLian]

Client requests don’t seem to be so similar, they should all be placed in one.