Вы можете использовать регулярное выражение
import re
data = '''
(script type="text/javascript">window._sharedData = {"config":{"csrf_token":"hIuZDxW17bTXz5EDLY25ftqivOOrLEeZ","viewer":null,"viewerId":null},"supports_es6":false,"country_code":"RU","language_code":"en","locale":"en_US","entry_data":{"PostPage":[{"graphql":{"shortcode_media":{"__typename":"GraphImage","id":"1968747493659350883","shortcode":"BtSZWokAZdj","dimensions":{"height":640,"width":640},"gating_info":null,"media_preview":"ACoq5miitSxxIGTHPXPGcd8ZFAGXRXSSWypFsAAZ/lzjpn/Csm5sjAu7Ib8MUAUaKU0lABVq0lMUqsPUA/Q8VVpynBB9CKAOtuOFB9CD+uP5Gq19HuiOPTP5Ul1exhdgy7kdF7fU/wCGatJiRPqv5ZFIZybnP4UynOpUlT1HFNpiClDFeRSUUATLcSJ904+lPF5MvR2H41WooAc7lzuY5J702iigD//Z","display_url":"https://instagram.fhel3-1.fna.fbcdn.net/vp/68311f4b09669fd75609e9fcabbf1ae0/5D0517DE/t51.2885-15/e35/49907137_294327238101721_6745007497573009307_n.jpg?_nc_ht=instagram.fhel3-1.fna.fbcdn.net","display_resources":[{"src":"https://instagram.fhel3-1.fna.fbcdn.net/vp/68311f4b09669fd75609e9fcabbf1ae0/5D0517DE/t51.2885-15/e35/49907137_294327238101721_6745007497573009307_n.jpg?_nc_ht=instagram.fhel3-1.fna.fbcdn.net","config_width":640,"config_height":640},{"src":"https://instagram.fhel3-1.fna.fbcdn.net/vp/68311f4b09669fd75609e9fcabbf1ae0/5D0517DE/t51.2885-15/e35/49907137_294327238101721_6745007497573009307_n.jpg?_nc_ht=instagram.fhel3-1.fna.fbcdn.net","config_width":750,"config_height":750},{"src":"https://instagram.fhel3-1.fna.fbcdn.net/vp/68311f4b09669fd75609e9fcabbf1ae0/5D0517DE/t51.2885-15/e35/49907137_294327238101721_6745007497573009307_n.jpg?_nc_ht=instagram.fhel3-1.fna.fbcdn.net","config_width":1080,"config_height":1080}],"accessibility_caption":"Image may contain: one or more people and closeup","is_video":false,"should_log_client_event":false,"tracking_token":"eyJ2ZXJzaW9uIjo1LCJwYXlsb2FkIjp7ImlzX2FuYWx5dGljc190cmFja2VkIjp0cnVlLCJ1dWlkIjoiN2Q1Yjg2NmY5OGIwNDVhNWIxMmRhNjEwZTA3NDY1MmYxOTY4NzQ3NDkzNjU5MzUwODgzIn0sInNpZ25hdHVyZSI6IiJ9","edge_media_to_tagged_user":{"edges":[]},"edge_media_to_caption":{"edges":[{"node":{"text":"\u2022\nScars show your story. \nYour pain. \nYour hate.\nYour sadness and despair. \nThey make you who you are, and one of a kind with every different mark. \nSome stay, some go.\nSome brighter, some lighter.\nSome bigger, some smaller.\nSome deeper, some one the surface. \nBut they are really all the same, you see?\nThey are all scars, just telling different points of our life, our story. \nOur souvenir throughout our whole life, that shows us how much we've grown. \nHow much we have overcome. How strong we've become.\nHow brave and courageous we've become from the hardest and darkest times of our life. \u2022\n\u2022\n\u2022\n\u2022\n#poem #cuts #selfharm #tatoo #dark #pain #sad #lonely #anxiety #depressed"}}]},"caption_is_edited":true,"has_ranked_comments":false,"edge_media_to_comment":{"count":1,"page_info":{"has_next_page":false,"end_cursor":null},"edges":[]},"comments_disabled":false,"taken_at_timestamp":1548913011,"edge_media_preview_like":{"count":17,"edges":[]},"edge_media_to_sponsor_user":{"edges":[]},"location":null,"viewer_has_liked":false,"viewer_has_saved":false,"viewer_has_saved_to_collection":false,"viewer_in_photo_of_you":false,"viewer_can_reshare":true,"owner":{"id":"10173498181","is_verified":false,"profile_pic_url":"https://instagram.fhel3-1.fna.fbcdn.net/vp/9a17134e8d0a36efec53f1da5cac1f38/5D14BC0F/t51.2885-19/s150x150/47690762_475199173011446_4764198224049209344_n.jpg?_nc_ht=instagram.fhel3-1.fna.fbcdn.net","username":"devils..tea.","blocked_by_viewer":false,"followed_by_viewer":false,"full_name":"depressed\ud83e\udd40","has_blocked_viewer":false,"is_private":false,"is_unpublished":false,"requested_by_viewer":false}......
'''
r = re.compile(r'username":"(.*)(?=","blocked)')
print(r.findall(data))