Python study notes (10) -- combined data type (collection type)

Collection type

A set is an unordered combination of multiple elements, each element is unique, does not exist of the same type, and each element is an immutable type. It is represented by {}, and the elements are separated by commas. Use {} to create a combined type, or the set function. If it is an empty set, you must use set.

>>> a={'a','b'}
>>> a
{'a', 'b'}
>>> b=set("pypy123")
>>> b
{'p', '2', 'y', '1', '3'}

Set operator:

S|T returns a new set containing all elements in sets S and T

ST includes elements in set S but not in T

S&T includes elements in both sets S and T

S^T includes non-identical elements in sets S and T

S<=T or S<T returns True/False to judge the subset relationship between S and T

S>=T or S>T returns True/False, judging the inclusion relationship between S and T

Enhanced operator:

S |=T

S -=T

S &= T

S ^=T

Collection processing method:

S.add(x) if x is not in S, add x to S

S.discard(x) removes the element x in S, if x is not in the set, no error is reported

S.remove(x) removes the element x in S, if x is not in the set, a KeyError exception is generated

S.clear() removes all elements in S

S.pop() randomly returns an element of S, updates S, if S is empty, a KeyError exception is generated

S.copy() returns a copy of S

len(S) returns the number of elements in the collection

x in S is in, return True

x not in S does not return True

set(x) converts the x variable to a collection type

>>> b
{'2', 'y', '1', '3'}
>>> try:
       while True:
          print(b.pop(),end="")
    except:
       pass
2y13
>>> b
set()

Collection type application scenarios:

Inclusion relation comparison: 'p' in {'p','y',123} {'p', 'y'} >= {'p','y',123}

Data deduplication : Convert a list type with repeated elements to a collection type without repeated elements. If you need to use a list type, convert the collection type to a list type

>>> ls=['p', 'y', 'y', 'p', 123]
>>> ls
['p', 'y', 'y', 'p', 123]
>>> s=set(ls)
>>> s
{'y', 123, 'p'}
>>> It=list(s)
>>> It
['y', 123, 'p']