# tuple: is a list which elements can't be modified

# if condition_test:
#     do something

# if condition_test:
#     do something
# else:
#     do something

# if condition1:
#     do something
# elif condition2:
#     do something
# elif condition3:
#     do something
# else:
#     do something

# if list is null([]), will return False, otherwise return True

## dictionary: {key:value, key1:value1, ...}
#  dict.keys()   dict.items() dict.values()
#  for key in dict.keys() == for key in dict
#  for key, value in dict.items()
#  for value in dict.values()
#  dict.values() will return a value list, but maybe has the same value,
#  we can use set(dict.values()) to remove the same values, just reserve one.

## dictionary list
#  dictionary can contain a object information, for example
#  users = {
#      'name':'Tom',
#      'addr':'US',
#      'age': 25,
#      'token': '001',
#      }
# list = [users]
# print(list[0]['age'])

## use list in dictionary
#  for example,
#  pizza = {
#      'crust': 'thick',
#      'toppings': ['mushrooms', 'extra cheese'],
#      }

## use dictionary in dictionary
