python-7 dict

dict 去重，存放后面的值。key不可为list，value可为list。

dict() 里使用这种写法语法不对，需标识符，‘1’ 和 1 不是标识符。

set 设置，如果没kv对，则使用当前这个key构建一个kv对，value没写用 None并返回当前的value值；如果有kv对，返回原本的value值。

‘b’ 需先定义 value存放的是引用地址

删除是把引用计数减一，当引用计数清零后，在适当时机垃圾回收机制启动，发现这个引用计数为零，标记为垃圾并将其清理掉。

for 里面允许修改值，但长度不能变化。使用到keys values items ，就不能进行kv对增加和kv对减少

从3.6 按录入序记录，但实际hash值千差万别

from collections import defaultdict 

num = '   00000147923522462300572245063134543617   '.strip().lstrip('0')
d1 = defaultdict(int)

for k in num:
    d1[k] += 1 
    
print(d1)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
num = '   00000147923522462300572245063134543617   '.strip().lstrip('0')
counter = {}

# for c in num:
#     if c in counter.keys():
#         counter[c] += 1 
#     else: 
#         counter[c] = 1 


# for c in num:   # O(n)
#     if not c in counter.keys():   #O(1)
#         counter[c] = 0 
#     counter[c] += 1 
    
for c in num:
    counter[c] = counter.get(c, 0) + 1 

print(counter)

from collections import defaultdict,OrderedDict
import random

l1 = []
d1 = defaultdict(int)

for i in range(100):
    l1.append(random.randint(-1000,1000))
    

l1.sort()
for k in l1:
    d1[k] += 1 
    
print(d1)

import random

# nums = []
# for i in range(100):
#     nums.append(random.randint(-1000,1000)

n = 100
nums = [None] * n 
for i in range(n):
    nums[i] = random.randint(-1000,1000)
    
counter = {}
for x in nums:
    counter[x] = counter.get(x, 0) + 1 

# keys = list(counter.keys())
# keys.sort()
# for k in keys:
#     print(k, counter[k])
    
keys = sorted(counter.keys())
for k in keys:
    print(k, counter[k])
    
# sorted 返回一个新的列表
print(sorted(counter.items()))  # 默认情况会以二元组的索引0的数据排序

from collections import defaultdict 
import random

alphabet = 'abcdefghijklmnopqrstuvwxyz'
l1 = []
d1 = defaultdict(int)
# char = random.choice(alphabet)   #随机取一个字符
# print(char)

for i in range(100):
    char = "".join(random.sample(alphabet,2))   # 随机取指定个数的字符
    l1.append(char)

sorted(l1,reverse=True)
for k in l1:
    d1[k] += 1 
    
print(d1)

import random

alphabet = 'abcdefghijklmnopqrstuvwxyz'

names = []
for i in range(100):
    names.append(random.choice(alphabet) + random.choice(alphabet))  #  同一个字符可以取两次
    # names.append("".join(random.sample(alphabet, k=2)))   #  同一个字符只取一次

counter= {} 
for name in names:
    counter[name] = counter.get(name, 0) + 1 
print(sorted(counter.items(), reverse=True))