import json

owner_id = ['owner1', 'owner2', 'owner3', 'owner2']
media_id = ['media1', 'media2', 'media3', 'media4']

result = []

for owner, media in zip(owner_id, media_id):
    result.append({"owner": owner, "media": media})

unique = {item['owner']: item for item in result}
print(unique)

# output: 
# {
# 'owner1': {'owner': 'owner1', 'media': 'media1'},
# 'owner2': {'owner': 'owner2', 'media': 'media4'},
# 'owner3': {'owner': 'owner3', 'media': 'media3'}
# }