Saving UTF-8 CSV with Python

I've been struggling with this, and have read numerous threads, but I can't seem to get this working. I need to save a UTF-8 CSV file.

Firstly, here's my super-simple approach:

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import csv
import sys
import codecs

f = codecs.open("output.csv", "w", "utf-8-sig")
writer = csv.writer(f, delimiter=',', quotechar='"', quoting=csv.QUOTE_MINIMAL)
cells = ["hello".encode("utf-8"), "nǐ hǎo".encode("utf-8"), "你好".encode("utf-8")]
writer.writerow(cells)

That results in an error:

Traceback (most recent call last):
  File "./makesimplecsv.py", line 10, in <module>
    cells = ["hello".encode("utf-8"), "nǐ hǎo".encode("utf-8"), "你好".encode("utf-8")]
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc7 in position 1: ordinal not in range(128)

I've also tried using the UnicodeWriter class that's listed in the Python docs (https://docs.python.org/2/library/csv.html#examples ):

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import csv
import sys
import codecs
import cStringIO

class UnicodeWriter:
    """
    A CSV writer which will write rows to CSV file "f",
    which is encoded in the given encoding.
    """

    def __init__(self, f, dialect=csv.excel, encoding="utf-8", **kwds):
        # Redirect output to a queue
        self.queue = cStringIO.StringIO()
        self.writer = csv.writer(self.queue, dialect=dialect, **kwds)
        self.stream = f
        self.encoder = codecs.getincrementalencoder(encoding)()

    def writerow(self, row):
        self.writer.writerow([s.encode("utf-8") for s in row])
        # Fetch UTF-8 output from the queue ...
        data = self.queue.getvalue()
        data = data.decode("utf-8")
        # ... and reencode it into the target encoding
        data = self.encoder.encode(data)
        # write to the target stream
        self.stream.write(data)
        # empty queue
        self.queue.truncate(0)

    def writerows(self, rows):
        for row in rows:
            self.writerow(row)

f = codecs.open("output.csv", "w", "utf-8-sig")
writer = UnicodeWriter(f)
cells = ["hello".encode("utf-8"), "nǐ hǎo".encode("utf-8"), "你好".encode("utf-8")]
writer.writerow(cells)

That results in the same error:

Traceback (most recent call last):
  File "./makesimplecsvwithunicodewriter.sh", line 40, in <module>
    cells = ["hello".encode("utf-8"), "nǐ hǎo".encode("utf-8"), "你好".encode("utf-8")]
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc7 in position 1: ordinal not in range(128)

I thought I'd gone through the checklist of things I've found in other similar questions:

• My file has an encoding statement.
• I'm opening the file for writing with UTF-8.
• I'm encoding the individual strings in UTF-8 before I pass them to the CSV writer.
• I've tried with and without adding a UTF-8 BOM, but that doesn't seem to make any difference, or indeed be critical, from what I've read.

Any ideas on what I'm doing wrong?