1.检查给定列表是不是存在重复元素
def all_unique(lst):
return len(lst) == len(set(lst))
x = [1, 1, 2, 2, 3, 2, 3, 4, 5, 6]
y = [1, 2, 3, 4, 5]
all_unique(x) # False
all_unique(y) # True
2.检查两个字符串的组成元素是不是一样的
from collections import Counter
def anagram(first, second):
return Counter(first) == Counter(second)
anagram("abcd3", "3acdb") # True
3.内存占用
import sys
variable = 30
print(sys.getsizeof(variable)) # 28
4.检查字符串占用的字节数
def byte_size(string):
return (len(string.encode('utf-8')))
byte_size('') # 4
byte_size('Hello World') # 11
5.打印 N 次字符串
n = 2
s = "Programming"
print(s * n)
6.大写第一个字母
s = "programming is awesome"
print(s.title()) # Programming Is Awesome
7.给定具体的大小，定义一个函数以按照这个大小切割列表
from math import ceil
def chunk(lst, size):
return list(
map(lambda x: lst[x * size:x * size + size],
list(range(0, ceil(len(lst) / size)))))
chunk([1, 2, 3, 4, 5], 2) # [[1,2],[3,4],5]
8.这个方法可以将布尔型的值去掉，例如（False，None，0，“”），它使用 filter() 函数
def compact(lst):
return list(filter(bool, lst))
compact([0, 1, False, 2, '', 3, 'a', 's', 34]) # [ 1, 2, 3, 'a', 's', 34 ]
9.如下代码段可以将打包好的成对列表解开成两组不同的元组
array = [['a', 'b'], ['c', 'd'], ['e', 'f']]
transposed = zip(*array)
print(transposed) # [('a', 'c', 'e'), ('b', 'd', 'f')]
10.我们可以在一行代码中使用不同的运算符对比多个不同的元素
a = 3
print(2 < a < 8) # True
print(1 == a < 2) # False
11.将列表连接成单个字符串，且每一个元素间的分隔方式设置为了逗号
hobbies = ["basketball", "football", "swimming"]
print("My hobbies are: " + ", ".join(hobbies)) # My hobbies are: basketball, football, swimming
12.统计字符串中的元音 (‘a’, ‘e’, ‘i’, ‘o’, ‘u’) 的个数，它是通过正则表达式做的
import re
def count_vowels(str):
return len(re.findall(r'[aeiou]', str, re.IGNORECASE))
count_vowels('foobar') # 3
count_vowels('gym') # 0
13.给定字符串的第一个字符统一为小写
def decapitalize(string):
return string[:1].lower() + string[1:]
decapitalize('FooBar') # 'fooBar'
decapitalize('FooBar') # 'fooBar'
14.通过递归的方式将列表的嵌套展开为单个列表
def spread(arg):
ret = []
for i in arg:
if isinstance(i, list):
ret.extend(i)
else:
ret.append(i)
return ret
def deep_flatten(lst):
result = []
result.extend(
spread(list(map(lambda x: deep_flatten(x) if type(x) == list else x, lst))))
return result
print(deep_flatten([1, [2], [[3], 4], 5])) # [1,2,3,4,5]
15.返回第一个列表的元素，其不在第二个列表内。如果同时要反馈第二个列表独有的元素，还需要加一句 set_b.difference(set_a)
def difference(a, b):
set_a = set(a)
set_b = set(b)
comparison = set_a.difference(set_b)
return list(comparison)
difference([1, 2, 3], [1, 2, 4]) # [3]
16.如下方法首先会应用一个给定的函数，然后再返回应用函数后结果有差别的列表元素
from math import floor
def difference_by(a, b, fn):
b = set(map(fn, b))
return [item for item in a if fn(item) not in b]
print(difference_by([2.1, 1.2], [2.3, 3.4], floor)) # [1.2]
print(difference_by([{'x': 2}, {'x': 1}], [{'x': 1}], lambda v: v['x'])) # [ { x: 2 } ]
17.你可以在一行代码内调用多个函数
def add(a, b):
return a + b
def subtract(a, b):
return a - b
a, b = 4, 5
print((subtract if a > b else add)(a, b)) # 9
18.检查两个列表是不是有重复项
def has_duplicates(lst):
return len(lst) != len(set(lst))
x = [1, 2, 3, 4, 5, 5]
y = [1, 2, 3, 4, 5]
print(has_duplicates(x)) # True
print(has_duplicates(y)) # False
19.合并两个字典
def merge_two_dicts(a, b):
c = a.copy() # make a copy of a
c.update(b) # modify keys and values of a with the once from b
return c
a = {'x': 1, 'y': 2}
b = {'y': 3, 'z': 4}
print(merge_two_dicts(a, b)) # {'y':3,'x':1,'z':4}
def merge_dictionaries(a, b):
return {**a, **b}
a = {'x': 1, 'y': 2}
b = {'y': 3, 'z': 4}
print(merge_dictionaries(a, b)) # {'y': 3, 'x': 1, 'z': 4}
20.两个列表转化为单个字典
def to_dictionary(keys, values):
return dict(zip(keys, values))
keys = ["a", "b", "c"]
values = [2, 3, 4]
print(to_dictionary(keys, values)) # {'a': 2, 'c': 4, 'b': 3}
21.我们常用 For 循环来遍历某个列表，同样我们也能枚举列表的索引与值
list = ["a", "b", "c", "d"]
for index, element in enumerate(list):
print("Value", element, "Index ", index, )
# ('Value', 'a', 'Index ', 0)
# ('Value', 'b', 'Index ', 1)
# ('Value', 'c', 'Index ', 2)
# ('Value', 'd', 'Index ', 3)
22.计算执行特定代码所花费的时间
import time
start_time = time.time()
a = 1
b = 2
c = a + b
print(c) # 3
end_time = time.time()
total_time = end_time - start_time
print("Time: ", total_time) # ('Time: ', 1.1205673217773438e-05)
23.我们在使用 try/except 语句的时候也可以加一个 else 子句，如果没有触发错误的话，这个子句就会被运行
try:
2 * 3
except TypeError:
print("An exception was raised")
else:
print("Thank God, no exceptions were raised.") # Thank God, no exceptions were raised.
24.根据元素频率取列表中最常见的元素
def most_frequent(list):
return max(set(list), key=list.count)
list = [1, 2, 1, 2, 3, 2, 1, 4, 2]
print(most_frequent(list)) # 2
25.检查给定的字符串是不是回文序列，它首先会把所有字母转化为小写，并移除非英文字母符号。最后，它会对比字符串与反向字符串是否相等，相等则表示为回文序列
from re import sub
def palindrome(string):
s = sub('[W_]', '', string.lower())
return s == s[::-1]
print(palindrome('taco cat')) # True
26.不使用条件语句就实现加减乘除、求幂操作，它通过字典这一数据结构实现
import operator
action = {
"+": operator.add,
"-": operator.sub,
"/": operator.truediv,
"*": operator.mul,
"**": pow
}
print(action['-'](50, 25)) # 25
27.该算法会打乱列表元素的顺序，它主要会通过 Fisher-Yates 算法对新列表进行排序
from copy import deepcopy
from random import randint
def shuffle(lst):
temp_lst = deepcopy(lst)
m = len(temp_lst)
while (m):
m -= 1
i = randint(0, m)
temp_lst[m], temp_lst[i] = temp_lst[i], temp_lst[m]
return temp_lst
foo = [1, 2, 3]
print(shuffle(foo)) # [2,3,1] , foo = [1,2,3]
28.将列表内的所有元素，包括子列表，都展开成一个列表
def spread(arg):
ret = []
for i in arg:
if isinstance(i, list):
ret.extend(i)
else:
ret.append(i)
return ret
print(spread([1, 2, 3, [4, 5, 6], [7], 8, 9])) # [1,2,3,4,5,6,7,8,9]
29.不需要额外的操作就能交换两个变量的值
def swap(a, b):
return b, a
a, b = -1, 14
print(swap(a, b)) # (14, -1)
30.通过 Key 取对应的 Value 值，可以通过以下方式设置默认值。如果 get() 方法没有设置默认值，那么如果遇到不存在的 Key，则会返回 None
d = {'a': 1, 'b': 2}
print(d.get('c', 3)) # 3