What is really the difference between += operation and append function in python lists? inside functions definations [duplicate]

Question

So till now the only real difference that I knew about the difference in the append and += operation was that of speed but recently I stumbled upon a case in which += would throw an error while append would not can someone help out with what has been happening?

This code would not run and throw an error namely UnboundLocalError: local variable 'travel_log' referenced before assignment

travel_log = [
{
  "country": "France",
  "visits": 12,
  "cities": ["Paris", "Lille", "Dijon"]
},
{
  "country": "Germany",
  "visits": 5,
  "cities": ["Berlin", "Hamburg", "Stuttgart"]
},
]

def add_new_country(Country,Visits,Cities):
    travel_log+={"country":Country,"visits":Visits,"cities":Cities}

add_new_country("Russia", 2, ["Moscow", "Saint Petersburg"])
print(travel_log)

while this code would run

travel_log = [
{
  "country": "France",
  "visits": 12,
  "cities": ["Paris", "Lille", "Dijon"]
},
{
  "country": "Germany",
  "visits": 5,
  "cities": ["Berlin", "Hamburg", "Stuttgart"]
},
]

def add_new_country(Country,Visits,Cities):
    travel_log.append({"country":Country,"visits":Visits,"cities":Cities})

add_new_country("Russia", 2, ["Moscow", "Saint Petersburg"])
print(travel_log)

Answer 1

While using the operator '+', you should create the list

travel_log = []

before using it.

def add_new_country(Country,Visits,Cities):
travel_log = []
travel_log+={"country":Country,"visits":Visits,"cities":Cities}