Dictionary

A dictionary can be created using curly braces {} or the dict function. Note that you cannot use dictionary comprehension to create a dictionary in Python Parser.

• Method 1: Creating a dictionary using curly braces {}.

  // method 1: curly braces {}
  d = {'A':12, 'B':`halo, 'C': [1,2,3]}
  type(d)

  Output: dict

  d1 = {'alpha':{'A': 1, 'B': 2}, 'num':{1: 2, 2: 3}}

  Output: {'alpha': {'A': 1, 'B': 2}, 'num': {1: 2, 2: 3}}

• Method 2: Creating a dictionary using the dict function.

  // method 2: dict(iterable, **kwarg)
  d1 = dict([('one', 1), ('two', 2), ('three', 3)]) 
  type(d1)

  Output: dict

Access a dictionary item by referring to its key name.

d['C']

Output: [1,2,3]

d.values()

1. Changing dictionary items

   d['B'] = 2022.01.01
   d

   Output: {'A': 12, 'B': 2022.01.01, 'C': [1, 2, 3]}

   d2 = {'A':15, 'D':`YES}
   d.update(d2)
   d

   Output: {'A': 15, 'B': 2022.01.01, 'C': [1, 2, 3], 'D': 'YES'}

2. Adding dictionary items

   d = {'A':12, 'B':`halo, 'C': [1,2,3]}
   d['D'] = ("math", "chinese", [90, 80])
   d

   Output: {'A': 12, 'B': 'halo', 'C': [1, 2, 3], 'D': ('math', 'chinese', [90, 80])}

3. Removing dictionary items

   d = {'A':12, 'B':`halo, 'C': [1,2,3]}
   d.pop('A')  // Remove the item with the specified key name

   Output: 12

   d

   Output: {'B': 'halo', 'C': [1, 2, 3]}

   d.clear()
   d

   Output: {}

dir(d)

Output: ['__dir__', '__eq__', '__getitem__', '__init__', '__iter__', '__len__', '__ne__', '__repr__', '__req__', '__rne__', '__str__', 'clear', 'copy', 'fromkeys', 'get', 'items', 'keys', 'pop', 'setdefault', 'toddb', 'update', 'values']

If all keys in a Python Parser dictionary share the same data type and are not of type DOUBLE or FLOAT, you can use toddb, a unique method in Python Parser, to convert this dictionary object into a DolphinDB dictionary.

d = {'A': 12, 'B': 2022.01.01, 'C': [1, 2, 3]}
type(d.toddb())

Output: dolphindb.DICTIONARY.STRING

d = {1: 12, 2: 2022.01.01, 3: [1, 2, 3]}
type(d.toddb())

Output: dolphindb.DICTIONARY.INT