자료구조 : 딕셔너리

딕셔너리 (dictionary)

• 딕셔너리
  value of key can't be changed
  value of key can't be duplicated in the same dictionary (if you do, the value of key can be overwritten of the new one.)

• 딕셔너리 생성
  key values can't be duplicated,but value values can be duplicated.

  Ex.

  ```
  my_dic = {}
  my_dic = dict()
  my_dic = {'a':111, 'b':222, 'c':333, 'd':444}   
  ```

• 데이터 조회
  - access with key

  Ex.

  ```
  pro_dic = { 
    'name' : 'DRAM',
    'capa' : '32g',
    'maker' : 'SK',
    'price' : 320000
  }
  print(pro_dic.get('name')) 	# get(key)
  print(pro_dic['name'])		# dict[key]
  ```

  By using 'in' function, you can check if the key value is in that dictionary

  Ex.

  ```
  print('maker' in pro_dic) 	# True
  print('price' in pro_dic)	# True
  print('ssn' in pro_dic)		# False
  ```

• 값 추가
  - dict1.update(dict2) : insert dict2 at the end of the dict1

  Ex.

  ```
  pro_dic['ssn'] = 1234
  print(pro_dic)
  ####################################################
  add_info = {
  	'loc': '이천',
  	'pop': 33
  }
  pro_dic.update(add_info)
  print(pro_dic)
  ```

  ㄴ> 출력 값

  ```
  {'name': 'DRAM', 'capa': '32g', 'maker': 'SK', 'price': 320000, 'ssn': 1234}
  {'name': 'DRAM', 'capa': '32g', 'maker': 'SK', 'price': 320000, 'ssn': 1234, 'loc': '이천', 'pop': 33}
  ```

• 값 수정

  Ex.

  ```
  pro_dic[price] = 230000
  print(pro_dic)
  ```

  ㄴ> 출력 값

  ```
  {'name': 'DRAM', 'capa': '32g', 'maker': 'SK', 'price': 230000, 'ssn': 1234, 'loc': '이천', 'pop': 33}
  ```

• 데이터 삭제
  - del dict[key1] : delete a key-value element that has a key value of key1
  - pop(key1) : delete a key-value element that has a key value of key1
  - clear() : delete all elements in that dictionary

  Ex.

  ```
  del pro_dic['loc']
  pro_dic.pop('pop')
  pro_dic.clear()
  ```

• 딕셔너리 함수 etc ... (keys, values, items, ...)
  - keys() : return all key values in that dictionary (return type : dict_keys)
  - values() : return all value values in that dictionary (return type : dict_values)
  - items() : return tuple(key, value) in that dictionary (return type : dict_items)

  Ex.

  ```
  my_dic = {
  	'name': 'James',
  	'age': 34,
  	'address': 'Texas',
  	'phone': '123456'
  }
  my_keys = my_dic.keys()
  my_keys = list(my_keys)
  print(my_keys)
  #
  my_values = my_dic.values()
  my_values = list(my_values)
  print(my_values)
  #
  my_items = my_dic.items()
  my_items = list(my_items)
  print(my_items)
  ```

  ㄴ> 출력값

  ```
  ['name', 'age', 'address', 'phone']
  ['James', 34, 'Texas', '123456']
  [('name', 'James'), ('age', 34), ('address', 'Texas'), ('phone', '123456')]
  ```