Set

Creating a Set

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

Method 1: Creating a set using curly braces {}.

// method 1: curly braces {}
st = {1,2,"3","4","5"}
type(st)

Output: set

Method 2: Creating a set using the set function.

// method 2: set([iterable])
st1 = set(['e', 'o', 'g', 'l'])
type(st1)

Output: set

Accessing Set Items

Set items cannot be accessed directly by referring to an index as they are unordered.

Updating a Set

Adding immutable set items
```
st.add("0")
st
```
Output: {1, 2, '3', '4', '5', '0'}
```
st.add([1,3,5])
```
Output: 'TypeError: unhashable type: 'list''
Updating a set by adding items from another set
```
st.update({'0', 1, 2, '4', '5', '6'})
st
```
Output: {1, 2, '3', '4', '5', '0', '6'}
Removing set items
- remove(): Remove the specified item from a set. If the specified item does not exist in the set, remove() will raise an error.
```
st.remove('3')
st
```
  Output: {1, 2, '4', '5', '0', '6'}
```
st.remove('7')
```
  Output: 'KeyError: "7"'
- discard(): Remove the specified item from a set. Different from remove(), discard() will not raise an error if the specified item does not exist in the set.
```
st = {1,2,"3","4","5"}
st.discard('4')
st
```
  Output: {1, 2, '3', '5'}
```
st.discard('4')   // Remove item '4' again. No error is raised though '4' does not exist.
st
```
  Output: {1, 2, '3', '5'}
- pop(): Remove a random item from a set and return the removed item.
```
st = {1,2,"3","4","5"}
st.pop()
```
  Output: 1
- clear(): Empty a set.
```
st = {1,2,"3","4","5"}
st.clear()
st
```
  Output: {}

Getting Available Attributes and Methods of a Set

dir(st)

Output: ['__bitAnd__', '__bitOr__', '__bitXor__', '__dir__', '__eq__', '__ge__', '__gt__', '__ibitAnd__', '__ibitOr__', '__ibitXor__', '__init__', '__isub__', '__iter__', '__le__', '__len__', '__lt__', '__ne__', '__repr__', '__req__', '__rne__', '__str__', '__sub__', 'add', 'clear', 'copy', 'difference', 'difference_update', 'discard', 'intersection', 'intersection_update', 'isdisjoint', 'issubset', 'issuperset', 'pop', 'remove', 'symmetric_difference', 'symmetric_difference_update', 'toddb', 'union', 'update']

toddb is a unique method in Python Parser, which supports converting a Python Parser set into a DolphinDB set. As DolphinDB set is strongly typed, the conversion through toddb fails if the types of items in a Python Parser set are not consistent.

st = {1,2,"3","4","5"}
type(st.toddb())

Output: TypeError: keyType can't be BOOL or ANY

st = {1, 2, 3, 4, 5}
type(st.toddb())

Output: dolphindb.SET.INT