set(), enumerate(), dict data structure

set()

nums=[1,1,2,3,3,4,5]
nums_set=set(nums)
print(nums_set)

{1, 2, 3, 4, 5}

nums_set.remove(4)
print(nums_set)

{1, 2, 3, 5}

nums_set.add(4)
print(nums_set)

{1, 2, 3, 4, 5}

enumerate()

seasons = ['Spring', 'Summer', 'Fall', 'Winter']
list(enumerate(seasons, start=1))

[(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]

for i, val in enumerate(seasons, start=1):
    print(i,val)

1 Spring
2 Summer
3 Fall
4 Winter

for i, val in enumerate(seasons, start=0):
    print(i,val)

0 Spring
1 Summer
2 Fall
3 Winter

The dict data structure

dic={'ID': 1, 'Name': 'alex','Phone':'805-xxx'}

print(dic['Name'])

alex

delete some term

del dic['Phone']
print(dic)

{'ID': 1, 'Name': 'alex'}

dic['Phone']='805'
print(dic)

{'ID': 1, 'Name': 'alex', 'Phone': '805'}

sorted(dic)

['ID', 'Name', 'Phone']

'ID' in dic

True

'address' not in dic

True

defaultdict

from collections import defaultdict
s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)]

d=defaultdict(list)
for k,val in s:
    d[k].append(val)
print(d)

dic={}
for k,val in s:
    dic[k]=val
print('dict:',dic)

defaultdict(<class 'list'>, {'yellow': [1, 3], 'blue': [2, 4], 'red': [1]})
dict: {'yellow': 3, 'blue': 4, 'red': 1}

one example like: containsDuplicate (Q217)

class Solution:
    def containsDuplicate(self, nums: List[int]) -> bool:
        from collections import defaultdict
        
        dic_check=defaultdict(int)
        
        for value in nums:
            if value in dic_check:
                return True
            else:
                dic_check[value]+=1
        return False

OrderedDict

from collections import OrderedDict

d = OrderedDict()
d['foo'] = 'python'
d['bar'] = 'spam'

d.items()

odict_items([('foo', 'python'), ('bar', 'spam')])

d['foo']

'python'

sorted() vs list.sort()

nums=[4,3,2,1,2,34,5,3]

print(sorted(nums))

print(nums)

[1, 2, 2, 3, 3, 4, 5, 34]
[4, 3, 2, 1, 2, 34, 5, 3]

nums.sort()

print(nums)

[1, 2, 2, 3, 3, 4, 5, 34]

seasons = ['Spring', 'Summer', 'Fall', 'Winter']
sorted(seasons)

['Fall', 'Spring', 'Summer', 'Winter']

### Counter from collections

from collections import Counter
counts=Counter('nagaram')
counts

Counter({'n': 1, 'a': 3, 'g': 1, 'r': 1, 'm': 1})

counts1=Counter('anagram')
counts1

Counter({'a': 3, 'n': 1, 'g': 1, 'r': 1, 'm': 1})

counts == counts1

True