def prepare_body(self, data, files, json=None):
        """Prepares the given HTTP body data."""

        # Check if file, fo, generator, iterator.
        # If not, run through normal process.

        # Nottin' on you.
        body = None
        content_type = None

        if not data and json is not None:
            # urllib3 requires a bytes-like body. Python 2's json.dumps
            # provides this natively, but Python 3 gives a Unicode string.
            content_type = 'application/json'
            body = complexjson.dumps(json)
            if not isinstance(body, bytes):
                body = body.encode('utf-8')

        is_stream = all([
            hasattr(data, '__iter__'),
            not isinstance(data, (basestring, list, tuple, Mapping))
        ])

        try:
            length = super_len(data)
        except (TypeError, AttributeError, UnsupportedOperation):
            length = None

        if is_stream:
            body = data

            if getattr(body, 'tell', None) is not None:
                # Record the current file position before reading.
                # This will allow us to rewind a file in the event
                # of a redirect.
                try:
                    self._body_position = body.tell()
                except (IOError, OSError):
                    # This differentiates from None, allowing us to catch
                    # a failed `tell()` later when trying to rewind the body
                    self._body_position = object()

            if files:
                raise NotImplementedError('Streamed bodies and files are mutually exclusive.')

            if length:
                self.headers['Content-Length'] = builtin_str(length)
            else:
                self.headers['Transfer-Encoding'] = 'chunked'
        else:
            # Multi-part file uploads.
            if files:
                (body, content_type) = self._encode_files(files, data)
            else:
                if data:
                    body = self._encode_params(data)
                    if isinstance(data, basestring) or hasattr(data, 'read'):
                        content_type = None
                    else:
                        content_type = 'application/x-www-form-urlencoded'

            self.prepare_content_length(body)

            # Add content-type if it wasn't explicitly provided.
            if content_type and ('content-type' not in self.headers):
                self.headers['Content-Type'] = content_type

        self.body = body
Prepares the given HTTP body data.
product/gradle-plugin/src/main/python/pip/_vendor/requests/models.py