Simple S3 download (for when boto is more than you need)

s3download.py

import base64
import hmac
import sha
import time
import urllib2

def download(access_key, secret_key, bucket, key, destination=None, timeout=None):
    url = 'http://%s.s3.amazonaws.com/%s' % (bucket, key)
    headers = _auth_header('GET', bucket, key, access_key, secret_key)
    data = urllib2.urlopen(
        urllib2.Request(url, headers=headers),
        timeout=timeout
    ).read()

    if destination is None:
        return data

    with open(destination, 'wb') as local_file:
        local_file.write(data)

def _auth_header(method, bucket, key, access_key, secret_key, amz_headers=None):
    ss = "{method}\n\n\n\n{amz_headers}\n{resource}"
    amz_headers = amz_headers or {}

    date = time.strftime("%a, %d %b %Y %X GMT", time.gmtime())
    amz_headers['x-amz-date'] = date

    # Header in format of "key:value\nkey:value" sorted by key
    header_string = '\n'.join(
        [':'.join([k, amz_headers[k]]) for k in sorted(amz_headers)]
    )

    sign_string = ss.format(
        method=method,
        amz_headers=header_string,
        resource='/'+bucket+'/'+key
    )

    auth_string = base64.encodestring(
        hmac.new(
            secret_key,
            sign_string,
            sha
        ).digest()).strip()

    headers = {
        'Authorization': 'AWS %s:%s' % (access_key, auth_string),
        'X-Amz-Date': date
    }
    return headers