Linked to from http://mause.me/blog/2014/03/21/python-requests-files.html

requests.py

files = {
    'unique_filename': 'file_data',
    'unique_filename': ('filename', 'file_data'),
    'unique_filename': ('filename', 'file_data', 'custom file content type'),
    'unique_filename': (
        'filename',
        'file_data',
        'custom file content type',
        <custom headers in tuple or dict>
    )
}

...

requests.post(<url>, files=files)