filepost

def choose_boundary():
    """
    Our embarrassingly-simple replacement for mimetools.choose_boundary.
    """
    boundary = binascii.hexlify(os.urandom(16))
    if not six.PY2:
        boundary = boundary.decode("ascii")
    return boundary

def encode_multipart_formdata(fields, boundary=None):
    """
    Encode a dictionary of ``fields`` using the multipart/form-data MIME format.

    :param fields:
        Dictionary of fields or list of (key, :class:`~urllib3.fields.RequestField`).

    :param boundary:
        If not specified, then a random boundary will be generated using
        :func:`urllib3.filepost.choose_boundary`.
    """
    body = BytesIO()
    if boundary is None:
        boundary = choose_boundary()

    for field in iter_field_objects(fields):
        body.write(b("--%s\r\n" % (boundary)))

        writer(body).write(field.render_headers())
        data = field.data

        if isinstance(data, int):
            data = str(data)  # Backwards compatibility

        if isinstance(data, six.text_type):
            writer(body).write(data)
        else:
            body.write(data)

        body.write(b"\r\n")

    body.write(b("--%s--\r\n" % (boundary)))

    content_type = str("multipart/form-data; boundary=%s" % boundary)

    return body.getvalue(), content_type

def iter_field_objects(fields):
    """
    Iterate over fields.

    Supports list of (k, v) tuples and dicts, and lists of
    :class:`~urllib3.fields.RequestField`.

    """
    if isinstance(fields, dict):
        i = six.iteritems(fields)
    else:
        i = iter(fields)

    for field in i:
        if isinstance(field, RequestField):
            yield field
        else:
            yield RequestField.from_tuples(*field)

def iter_fields(fields):
    """
    .. deprecated:: 1.6

    Iterate over fields.

    The addition of :class:`~urllib3.fields.RequestField` makes this function
    obsolete. Instead, use :func:`iter_field_objects`, which returns
    :class:`~urllib3.fields.RequestField` objects.

    Supports list of (k, v) tuples and dicts.
    """
    if isinstance(fields, dict):
        return ((k, v) for k, v in six.iteritems(fields))

    return ((k, v) for k, v in fields)