YouTipPython3 Set
# Python3.x Python3 Sets
A set is an unordered collection of unique elements.
Elements in a set are not repeated, and common set operations such as intersection, union, and difference can be performed.
You can create a set using curly braces `{ }`, with elements separated by commas `,`, or you can use the `set()` function to create a set.
**Creation Format:**
parame = {value01,value02,...} or set(value)
Here is a simple example:
set1 = {1, 2, 3, 4} # Create a set directly using curly braces set2 = set([4, 5, 6, 7]) # Create a set from a list using the set() function
**Note:** To create an empty set, you must use `set()` instead of `{ }`, because `{ }` is used to create an empty dictionary.
More examples:
## Example (Python 3.0+)
>>> basket ={'apple','orange','apple','pear','orange','banana'}
>>>print(basket)# This demonstrates the deduplication function
{'orange','banana','pear','apple'}
>>>'orange'in basket # Quickly check if an element is in the set
True
>>>'crabgrass'in basket
False
>>># The following demonstrates operations between two sets.
...
>>> a =set('abracadabra')
>>> b =set('alacazam')
>>> a
{'a','r','b','c','d'}
>>> a - b # Elements in set a but not in set b
{'r','d','b'}
>>> a | b # All elements in set a or b
{'a','c','r','d','b','m','z','l'}
>>> a & b # Elements common to both set a and b
{'a','c'}
>>> a ^ b # Elements not in the intersection of a and b
{'r','d','b','m','z','l'}
Similar to list comprehensions, sets also support set comprehensions:
## Example (Python 3.0+)
>>> a ={x for x in'abracadabra'if x not in'abc'}
>>> a
{'r','d'}
* * *
## Basic Set Operations
### 1. Adding Elements
**Syntax:**
s.add( x )
Adds element x to set s. If the element already exists, no action is taken.
## Example (Python 3.0+)
>>> thisset =set(("Google","","Taobao"))
>>> thisset.add("Facebook")
>>>print(thisset)
{'Taobao','Facebook','Google',''}
There is another method that can also add elements, and the parameter can be a list, tuple, dictionary, etc. The syntax is as follows:
s.update( x )
x can have multiple values, separated by commas.
## Example (Python 3.0+)
>>> thisset =set(("Google","","Taobao"))
>>> thisset.update({1,3})
>>>print(thisset)
{1,3,'Google','Taobao',''}
>>> thisset.update([1,4],[5,6])
>>>print(thisset)
{1,3,4,5,6,'Google','Taobao',''}
>>>
### 2. Removing Elements
**Syntax:**
s.remove( x )
Removes element x from set s. If the element does not exist, an error will occur.
## Example (Python 3.0+)
>>> thisset =set(("Google","","Taobao"))
>>> thisset.remove("Taobao")
>>>print(thisset)
{'Google',''}
>>> thisset.remove("Facebook")# An error will occur if it doesn't exist
Traceback (most recent call last):
File "", line 1,in
KeyError: 'Facebook'
>>>
There is another method to remove elements from a set, which does not cause an error if the element does not exist. The format is as follows:
s.discard( x )
## Example (Python 3.0+)
>>> thisset =set(("Google","","Taobao"))
>>> thisset.discard("Facebook")# No error occurs if it doesn't exist
>>>print(thisset)
{'Taobao','Google',''}
We can also randomly remove an element from the set. The syntax is as follows:
s.pop()
## Script Mode Example (Python 3.0+)