python snippets

1、Find memory used by an object

import sys
print(sys.getsizeof(5)) # 28
print(sys.getsizeof("Python")) # 55

2、Combine a list of strings into a single string

strings = [‘50‘, ‘python‘, ‘snippets‘]
print(‘,‘.join(strings)) # 50,python,snippets

3、Find elements that exist in either of the two lists

def union(a,b):
  return list(set(a + b))union([1, 2, 3, 4, 5], [6, 2, 8, 1, 4]) # [1,2,3,4,5,6,8]

4、Track frequency of elements in a list

from collections import Counter
list = [1, 2, 3, 2, 4, 3, 2, 3]
count = Counter(list)
print(count) # {2: 3, 3: 3, 1: 1, 4: 1}

5、Find the most frequent element in a list

def most_frequent(list):    # 原文取了set，不知道为什么也可以？
    return max(list, key = list.count)numbers = [1, 2, 3, 2, 4, 3, 1, 3]
most_frequent(numbers) # 3

 6、Use map functions

def multiply(n): 
    return n * n 
  
list = (1, 2, 3) 
result = map(multiply, list) 
print(list(result)) # {1, 4, 9}

 7、Use filter functions

arr = [1, 2, 3, 4, 5]
arr = list(filter(lambda x : x%2 == 0, arr))
print (arr) # [2, 4]

参考 https://medium.com/better-programming/25-useful-python-snippets-to-help-in-your-day-to-day-work-d59c636ec1b