How do i merge two json files in python?

I'm trying to do a python script that merge 2 json files for example:

First file: test.json

[
  {
    "user_id": "273631610",
    "item_id": "0829482",
    "rating": "7"
  },
  {
    "user_id": "40688800",
    "item_id": "1343092",
    "rating": "8"
  },
  {
    "user_id": "395680865",
    "item_id": "1453405",
    "rating": "8"
  }
]

Second file: test_userz.json

[
{"contributors": null, "truncated": false, "text": "", "in_reply_to_status_id": null, "id": 421040281296052225, "favorite_count": 0, "source": "IMDb Movies & TV on iOS", "retweeted": false, "coordinates": null, "entities": {"symbols": [], "user_mentions": [], "hashtags": [{"indices": [23, 28], "text": "IMDb"}], "urls": [{"url": "5E1fLOxB", "indices": [29, 51], "expanded_url": "http://www.imdb.com/title/tt0829482", "display_url": "imdb.com/title/tt0829482"}]}, "in_reply_to_screen_name": null, "id_str": "421040281296052225", "retweet_count": 0, "in_reply_to_user_id": null, "favorited": false, "user": {"follow_request_sent": false, "profile_use_background_image": true, "id": 273631610, "verified": false, "profile_text_color": "333333", "profile_image_url_https": "https://pbs.twimg.com/profile_images/378800000723050633/0fadb894b240dd426eb7b850dd8378d6_normal.jpeg", "profile_sidebar_fill_color": "DDEEF6", "is_translator": false, "geo_enabled": true, "entities": {"description": {"urls": []}}, "followers_count": 330, "protected": false, "location": "southend on sea", "default_profile_image": false, "id_str": "273631610", "lang": "en", "utc_offset": null, "statuses_count": 897, "description": "", "friends_count": 973, "profile_link_color": "0084B4", "profile_image_url": "http://pbs.twimg.com/profile_images/378800000723050633/0fadb894b240dd426eb7b850dd8378d6_normal.jpeg", "notifications": false, "profile_background_image_url_https": "https://abs.twimg.com/images/themes/theme1/bg.png", "profile_background_color": "C0DEED", "profile_background_image_url": "http://abs.twimg.com/images/themes/theme1/bg.png", "name": "Ben Morris", "is_translation_enabled": false, "profile_background_tile": false, "favourites_count": 12, "screen_name": "benyere", "url": null, "created_at": "Mon Mar 28 21:31:52 +0000 2011", "contributors_enabled": false, "time_zone": null, "profile_sidebar_border_color": "C0DEED", "default_profile": true, "following": false, "listed_count": 0}, "geo": null, "in_reply_to_user_id_str": null, "possibly_sensitive": false, "lang": "en", "created_at": "Wed Jan 08 22:06:40 +0000 2014", "in_reply_to_status_id_str": null, "place": null},
{"contributors": null, "truncated": false, "text": "", "in_reply_to_status_id": null, "id": 421040870931320833, "favorite_count": 0, "source": "iOS", "retweeted": false, "coordinates": null, "entities": {"symbols": [], "user_mentions": [], "hashtags": [{"indices": [31, 36], "text": "IMDb"}], "urls": [{"url": "dTFeexXDk", "indices": [37, 59], "expanded_url": "http://www.imdb.com/title/tt1343092", "display_url": "imdb.com/title/tt1343092"}]}, "in_reply_to_screen_name": null, "id_str": "421040870931320833", "retweet_count": 0, "in_reply_to_user_id": null, "favorited": false, "user": {"follow_request_sent": false, "profile_use_background_image": false, "id": 40688800, "verified": false, "profile_text_color": "333333", "profile_image_url_https": "https://pbs.twimg.com/profile_images/378800000807375392/2ee9bbee70e09ac097f8415794877e7c_normal.jpeg", "profile_sidebar_fill_color": "FFFFFF", "is_translator": false, "geo_enabled": true, "entities": {"description": {"urls": []}}, "followers_count": 230, "protected": false, "location": "Alexandria", "default_profile_image": false, "id_str": "40688800", "lang": "en", "utc_offset": 7200, "statuses_count": 8914, "description": "#TedxAlexandriaU head. resp of #emshi_fe_7artak in #alex Day dreamer. #medstudent by accident. I speak sarcasm.", "friends_count": 722, "profile_link_color": "0099CC", "profile_image_url": "http://pbs.twimg.com/profile_images/378800000807375392/2ee9bbee70e09ac097f8415794877e7c_normal.jpeg", "notifications": false, "profile_background_image_url_https": "https://si0.twimg.com/profile_background_images/778453690/27087117198cdf1d18bb86a36140de62.jpeg", "profile_background_color": "FFF04D", "profile_banner_url": "https://pbs.twimg.com/profile_banners/40688800/1378766815", "profile_background_image_url": "http://a0.twimg.com/profile_background_images/778453690/27087117198cdf1d18bb86a36140de62.jpeg", "name": "NOUR", "is_translation_enabled": false, "profile_background_tile": true, "favourites_count": 324, "screen_name": "Nour_Ayman", "url": null, "created_at": "Sun May 17 16:38:59 +0000 2009", "contributors_enabled": false, "time_zone": "Cairo", "profile_sidebar_border_color": "FFFFFF", "default_profile": false, "following": false, "listed_count": 2}, "geo": null, "in_reply_to_user_id_str": null, "possibly_sensitive": false, "lang": "en", "created_at": "Wed Jan 08 22:09:00 +0000 2014", "in_reply_to_status_id_str": null, "place": null},
{"contributors": null, "truncated": false, "text": "", "in_reply_to_status_id": null, "id": 421041098287755264, "favorite_count": 0, "source": "iOS", "retweeted": false, "coordinates": null, "entities": {"symbols": [], "user_mentions": [], "hashtags": [{"indices": [34, 39], "text": "IMDb"}], "urls": [{"url": "I2HqieyDnn", "indices": [40, 62], "expanded_url": "http://www.imdb.com/title/tt1453405", "display_url": "imdb.com/title/tt1453405"}]}, "in_reply_to_screen_name": null, "id_str": "421041098287755264", "retweet_count": 0, "in_reply_to_user_id": null, "favorited": false, "user": {"follow_request_sent": false, "profile_use_background_image": true, "id": 395680865, "verified": false, "profile_text_color": "333333", "profile_image_url_https": "https://pbs.twimg.com/profile_images/3130997221/4a981c8594f3c9ec127542ae40bac4ce_normal.jpeg", "profile_sidebar_fill_color": "DDEEF6", "is_translator": false, "geo_enabled": false, "entities": {"description": {"urls": []}}, "followers_count": 9, "protected": false, "location": "Denmark", "default_profile_image": false, "id_str": "395680865", "lang": "en", "utc_offset": 3600, "statuses_count": 1557, "description": "On basketball, film and other really cool things.", "friends_count": 27, "profile_link_color": "0084B4", "profile_image_url": "http://pbs.twimg.com/profile_images/3130997221/4a981c8594f3c9ec127542ae40bac4ce_normal.jpeg", "notifications": false, "profile_background_image_url_https": "https://abs.twimg.com/images/themes/theme1/bg.png", "profile_background_color": "C0DEED", "profile_background_image_url": "http://abs.twimg.com/images/themes/theme1/bg.png", "name": "Kristian Meller", "is_translation_enabled": false, "profile_background_tile": false, "favourites_count": 5, "screen_name": "kristianmeller", "url": null, "created_at": "Sat Oct 22 02:18:30 +0000 2011", "contributors_enabled": false, "time_zone": "Berlin", "profile_sidebar_border_color": "C0DEED", "default_profile": true, "following": false, "listed_count": 0}, "geo": null, "in_reply_to_user_id_str": null, "possibly_sensitive": false, "lang": "en", "created_at": "Wed Jan 08 22:09:55 +0000 2014", "in_reply_to_status_id_str": null, "place": null}
]

I would like to merge these into a single array like this:

[
{"user_id":"273631610","item_id":"0829482","rating":"7","contributors":null,"truncated":false,"text":"","in_reply_to_status_id":null,"id":421040281296052225,"favorite_count":0,"source":"IMDb Movies & TV on iOS<\/a>","retweeted":false,"coordinates":null,"entities":{"symbols":[],"user_mentions":[],"hashtags":[{"indices":[23,28],"text":"IMDb"}],"urls":[{"url":"/bk5E1fLOxB","indices":[29,51],"expanded_url":"http:\/\/www.imdb.com\/title\/tt0829482","display_url":"imdb.com\/title\/tt0829482"}]},"in_reply_to_screen_name":null,"id_str":"421040281296052225","retweet_count":0,"in_reply_to_user_id":null,"favorited":false,"user":{"follow_request_sent":false,"profile_use_background_image":true,"id":273631610,"verified":false,"profile_text_color":"333333","profile_image_url_https":"https:\/\/pbs.twimg.com\/profile_images\/378800000723050633\/0fadb894b240dd426eb7b850dd8378d6_normal.jpeg","profile_sidebar_fill_color":"DDEEF6","is_translator":false,"geo_enabled":true,"entities":{"description":{"urls":[]}},"followers_count":330,"protected":false,"location":"southend on sea","default_profile_image":false,"id_str":"273631610","lang":"en","utc_offset":null,"statuses_count":897,"description":"","friends_count":973,"profile_link_color":"0084B4","profile_image_url":"http:\/\/pbs.twimg.com\/profile_images\/378800000723050633\/0fadb894b240dd426eb7b850dd8378d6_normal.jpeg","notifications":false,"profile_background_image_url_https":"https:\/\/abs.twimg.com\/images\/themes\/theme1\/bg.png","profile_background_color":"C0DEED","profile_background_image_url":"http:\/\/abs.twimg.com\/images\/themes\/theme1\/bg.png","name":"Ben Morris","is_translation_enabled":false,"profile_background_tile":false,"favourites_count":12,"screen_name":"benyere","url":null,"created_at":"Mon Mar 28 21:31:52 +0000 2011","contributors_enabled":false,"time_zone":null,"profile_sidebar_border_color":"C0DEED","default_profile":true,"following":false,"listed_count":0},"geo":null,"in_reply_to_user_id_str":null,"possibly_sensitive":false,"lang":"en","created_at":"Wed Jan 08 22:06:40 +0000 2014","in_reply_to_status_id_str":null,"place":null},
{"user_id":"40688800","item_id":"1343092","rating":"8","contributors":null,"truncated":false,"text":"","in_reply_to_status_id":null,"id":421040281296052225,"favorite_count":0,"source":"IMDb Movies & TV on iOS<\/a>","retweeted":false,"coordinates":null,"entities":{"symbols":[],"user_mentions":[],"hashtags":[{"indices":[23,28],"text":"IMDb"}],"urls":[{"url":"/bk5E1fLOxB","indices":[29,51],"expanded_url":"http:\/\/www.imdb.com\/title\/tt0829482","display_url":"imdb.com\/title\/tt0829482"}]},"in_reply_to_screen_name":null,"id_str":"421040281296052225","retweet_count":0,"in_reply_to_user_id":null,"favorited":false,"user":{"follow_request_sent":false,"profile_use_background_image":true,"id":273631610,"verified":false,"profile_text_color":"333333","profile_image_url_https":"https:\/\/pbs.twimg.com\/profile_images\/378800000723050633\/0fadb894b240dd426eb7b850dd8378d6_normal.jpeg","profile_sidebar_fill_color":"DDEEF6","is_translator":false,"geo_enabled":true,"entities":{"description":{"urls":[]}},"followers_count":330,"protected":false,"location":"southend on sea","default_profile_image":false,"id_str":"273631610","lang":"en","utc_offset":null,"statuses_count":897,"description":"","friends_count":973,"profile_link_color":"0084B4","profile_image_url":"http:\/\/pbs.twimg.com\/profile_images\/378800000723050633\/0fadb894b240dd426eb7b850dd8378d6_normal.jpeg","notifications":false,"profile_background_image_url_https":"https:\/\/abs.twimg.com\/images\/themes\/theme1\/bg.png","profile_background_color":"C0DEED","profile_background_image_url":"http:\/\/abs.twimg.com\/images\/themes\/theme1\/bg.png","name":"Ben Morris","is_translation_enabled":false,"profile_background_tile":false,"favourites_count":12,"screen_name":"benyere","url":null,"created_at":"Mon Mar 28 21:31:52 +0000 2011","contributors_enabled":false,"time_zone":null,"profile_sidebar_border_color":"C0DEED","default_profile":true,"following":false,"listed_count":0},"geo":null,"in_reply_to_user_id_str":null,"possibly_sensitive":false,"lang":"en","created_at":"Wed Jan 08 22:06:40 +0000 2014","in_reply_to_status_id_str":null,"place":null},
{"user_id":"3956800865","item_id":"1453405","rating":"8","contributors":null,"truncated":false,"text":"","in_reply_to_status_id":null,"id":421040281296052225,"favorite_count":0,"source":"IMDb Movies & TV on iOS<\/a>","retweeted":false,"coordinates":null,"entities":{"symbols":[],"user_mentions":[],"hashtags":[{"indices":[23,28],"text":"IMDb"}],"urls":[{"url":"\/bk5E1fLOxB","indices":[29,51],"expanded_url":"http:\/\/www.imdb.com\/title\/tt0829482","display_url":"imdb.com\/title\/tt0829482"}]},"in_reply_to_screen_name":null,"id_str":"421040281296052225","retweet_count":0,"in_reply_to_user_id":null,"favorited":false,"user":{"follow_request_sent":false,"profile_use_background_image":true,"id":273631610,"verified":false,"profile_text_color":"333333","profile_image_url_https":"https:\/\/pbs.twimg.com\/profile_images\/378800000723050633\/0fadb894b240dd426eb7b850dd8378d6_normal.jpeg","profile_sidebar_fill_color":"DDEEF6","is_translator":false,"geo_enabled":true,"entities":{"description":{"urls":[]}},"followers_count":330,"protected":false,"location":"southend on sea","default_profile_image":false,"id_str":"273631610","lang":"en","utc_offset":null,"statuses_count":897,"description":"","friends_count":973,"profile_link_color":"0084B4","profile_image_url":"http:\/\/pbs.twimg.com\/profile_images\/378800000723050633\/0fadb894b240dd426eb7b850dd8378d6_normal.jpeg","notifications":false,"profile_background_image_url_https":"https:\/\/abs.twimg.com\/images\/themes\/theme1\/bg.png","profile_background_color":"C0DEED","profile_background_image_url":"http:\/\/abs.twimg.com\/images\/themes\/theme1\/bg.png","name":"Ben Morris","is_translation_enabled":false,"profile_background_tile":false,"favourites_count":12,"screen_name":"benyere","url":null,"created_at":"Mon Mar 28 21:31:52 +0000 2011","contributors_enabled":false,"time_zone":null,"profile_sidebar_border_color":"C0DEED","default_profile":true,"following":false,"listed_count":0},"geo":null,"in_reply_to_user_id_str":null,"possibly_sensitive":false,"lang":"en","created_at":"Wed Jan 08 22:06:40 +0000 2014","in_reply_to_status_id_str":null,"place":null}
]

To do that I did the following code:

import json

with open("test.json") as fin1:
    data1 = json.load(fin1)
with open("test_userz.json") as fin2:
    data2 = json.load(fin2)
data1.update(data2)
with open("merged.json", "w") as fout:
    json.dump(data1, fout)

but in runtime i see this error :

Traceback (most recent call last):
File "json/merge2jsons.py", line 7, in 
data1.update(data2)
AttributeError: 'list' object has no attribute 'update'

How can i do this merge ?