python常用极简代码

1. 重复元素判定

以下方法可以检查给定列表是不是存在重复元素，它会使用 set() 函数来移除所有重复元素。

#! /usr/bin/env python
# -*- coding: utf-8 -*-

def all_unique(lst):
    return len(lst) == len(set(lst))


x = [1, 1, 2, 3, 4, 5, 6, 4, 3, 2]
y = [1, 2, 3, 4, 5]
print(all_unique(x))  # False
print(all_unique(y))  # True

字符元素组成判定

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)


print(anagram("abcd3", "3acbd"))  # True

内存占用

import sys

variable = 30
print(sys.getsizeof(variable))  # 28

字节占用

def byte_size(string):
    return (len(string.encode("utf-8")))


print(byte_size(''))  # 0
print(byte_size("Hello World"))  # 11

打印N次字符串

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n = 5
s = "HHHHHH "
print(s * n)  # HHHHHH HHHHHH HHHHHH HHHHHH HHHHHH

大写第一个字母

1 2	s = "this is my blog" print(s.title()) # This Is My Blog

分块

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)))))


ret = chunk([1, 2, 3, 4, 5], 2)
print(ret)  # [[1, 2], [3, 4], [5]]

压缩

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))


print(compact([0, 1, False, 2, "", 3, "a", "s", 34]))  # [1, 2, 3, 'a', 's', 34]

解包

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array = [["a", "b"], ["c", "d"], ["e", "f"]]
transposed = zip(*array)
print(list(transposed))  # [('a', 'c', 'e'), ('b', 'd', 'f')]

链式对比

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a = 3
print(2 < a < 8)  # True
print(1 == a < 2)  # False

逗号连接

下面的代码可以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。

1 2	hobbies = ["basketball", "football", "swimming"] print("My hobbies are: " + ", ".join(hobbies)) # My hobbies are: basketball, football, swimming

首字母小写

def decapitalize(str):
    return str[:1].lower() + str[1:]

print(decapitalize("FooBar"))  # fooBar

展开列表

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]

列表的差集

该方法将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)

print(difference([1, 2, 3], [1, 2, 4]))  # [3]

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}]

链式函数调用

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

检查重复项

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

合并两个字典

def megre_two_dicts(a, b):
    c = a.copy()
    c.update(b)
    return c


a = {'x': 1, 'y': 2}
b = {'y': 3, 'z': 4}
print(megre_two_dicts(a, b))  # {'x': 1, 'y': 3, '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))  # {'x': 1, 'y': 3, 'z': 4}

将两个列表转化为字典

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, 'b': 3, 'c': 4}

使用枚举

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

执行时间

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:  2.6226043701171875e-06

Try else

try:
    2 * 3
except TypeError:
    print("An exception was raised")
else:
    print("Thand God, no exceptions were raised.")

# Thand God, no exceptions were raised.

元素频率

def mode_frequent(list):
    return max(set(list), key=list.count)


list = [1, 2, 3, 12, 4, 5, 6, 7, 23, 4, 5, 2]
print(mode_frequent(list))  # 2

回文序列

def palindrome(string):
    from re import sub
    s = sub('[\W_]', '', string.lower())
    return s == s[::-1]

print(palindrome('taco cat'))  # True

不使用 if-else 的计算子

import operator

action = {
    "+": operator.add,
    "-": operator.sub,
    "/": operator.truediv,
    "*": operator.mul,
    "**": pow
}
print(action['-'](50, 25))  # 25

Shuffle

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))  # [1,2,3]

展开列表

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]))

字典默认值

1 2	d = {"a": 1, "b": 2} print(d.get("c", 3)) # 3