版权声明：来自:陈海坤的博客(https://blog.csdn.net/chk218) https://blog.csdn.net/chk218/article/details/84886587
python中相对不常见却很实用的小窍门
空谈不如来码代码吧：
交换变量值
"""pythonic way of value swapping"""
a, b = 5, 10
print(a, b)
a, b = b, a
print(a, b)给列表元素创建新的分隔符
a = ["Python", "is", "awesome"]
print(" ".join(a))找列表中出现次数最多的元素
""" most frequent element in a list """
a = [1, 2, 3, 1, 2, 3, 2, 2, 4, 5, 1]
print(max(set(a), key=a.count))
""" using Counter from collections """
from collections import Counter
cnt = Counter(a)
print(cnt.most_common(3))核对两个字符是否为回文
from collections import Counter
str1 = "123456"
str2 = "654321"
if Counter(str1) == Counter(str2):
print("回文")
反向输出字符串
""" 方法一 """
a = "abcdefghijkmnopqrstuvwxyz"
print(a[::-1])
""" 方法二 """
for char in reversed(a):
print(char)
""" 方法三 """
num = 123456789
print(int(str(num)[::-1]))反向输出列表
""" 方法一 """
a = [5, 4, 3, 2, 1]
print(a[::-1])
""" 方法二 """
for i in reversed(a):
print(i)
转置2维数组
original = [['a', 'b'], ['c', 'd'], ['e', 'f']]
transposed = zip(*original)
print(list(transposed))
# [('a', 'c', 'e'), ('b', 'd', 'f')]链式比较
s = 6
print(3 < s < 8)
print(2 == s < 10)
# True
# False函数的链式写法
def product(a, b):
return a * b
def add(a, b):
return a + b
b = True
print((product if b else add)(5, 7))
# 35复制列表
a = [1, 2, 3, 4, 5]
b = a
b[0] = 10
print(b)
# [10, 2, 3, 4, 5]
b = a[:]
b[0] = 10
print(b)
# [10, 2, 3, 4, 5]
a = [1, 2, 3, 4, 5]
print(list(a))
# [1, 2, 3, 4, 5]
print(a.copy())
# [1, 2, 3, 4, 5]
from copy import deepcopy
l = [[1, 2], [3, 4]]
l2 = deepcopy(l)
print(l2)
# [[1, 2], [3, 4]]字典的添加
dicts = {'a': 1, 'b': 2}
print(dicts.get('c', 3))
# 3对字典的值排序
d = {'a': 10, 'b': 20, 'c': 5, 'd': 1}
print(sorted(d.items(), key=lambda x: x[1]))
# [('d', 1), ('c', 5), ('a', 10), ('b', 20)]
from operator import itemgetter
print(sorted(d.items(), key=itemgetter(1)))
# [('d', 1), ('c', 5), ('a', 10), ('b', 20)]
for else结构
a = [1, 2, 3, 4, 5]
for i in a:
if i == 0:
break
else:
print("did not break out of for loop")
将列表转换为逗号分隔
l = ['foo', 'bar', 'xyz']
print(','.join(l))
# foo,bar,xyz
num = [2, 3, 4, 5, 10]
print(','.join(map(str, num)))
# 2,3,4,5,10
data = [2, 'hello', 3, 3.4]
print(','.join(map(str, data)))
# 2,hello,3,3.4字典的合并
d1 = {'a': 1}
d2 = {'b': 2}
# pyhton 3.5
print({**d1, **d2})
# {'a': 1, 'b': 2}
print(dict(d1.items() | d2.items()))
# {'b': 2, 'a': 1}
d1.update(d2)
print(d1)
# {'a': 1, 'b': 2}
找列表中最大、最小值下标
li = [20, 50, 80, 10, 55]
def minIndex(li):
return min(range(len(li)), key=li.__getitem__)
def maxIndex(li):
return max(range(len(li)), key=li.__getitem__)
print(minIndex(li))
# 3
print(maxIndex(li))
# 2从列表中删除重复项
li = [2, 2, 3, 1, 3, 5, 6, 1]
newli = list(set(li))
print(newli)
# [1, 2, 3, 5, 6]
from collections import OrderedDict
li = ["foo", "bar", "bar", "foo"]
print(list(OrderedDict.fromkeys(li).keys()))
# ['foo', 'bar']all or any
x = [True, True, False]
if any(x):
print("至少有一个是True!")
if all(x):
print("没有一个是False！")
if any(x) and not all(x):
print("至少一个True和一个False！")
# 至少有一个是True!
# 至少一个True和一个False！emoji
from emoji import emojize
print(emojize(":thumbs_up"))**kwargs
dic = {'a': 1, 'b': 2}
def someFunction(a, b):
print(a + b)
return
someFunction(**dic)
someFunction(a=1, b=2)三元运算
a = 1
b = 5
if (a > b):
print(a)
else:
print(b)
print(a) if a > b else print(b)阶乘
i = 1
p = 1
n = input("输入：")
while i <= int(n):
p = p * i
i += 1
print("结果：" + str(p))
set(集合)数据结构
# set(集合)是一个非常有用的数据结构。它与列表(list)的行为类似，区别在于set不能包含重复的值。
# 这在很多情况下非常有用。例如你可能想检查列表中是否包含重复的元素，
# 你有两个选择，第一个需要使用for循环，就像这样：
some_list = ['a', 'b', 'c', 'b', 'd', 'm', 'n', 'n']
duplicates = []
for value in some_list:
if some_list.count(value) > 1:
if value not in duplicates:
duplicates.append(value)
print(duplicates)
# 输出: ['b', 'n']
# 但还有一种更简单更优雅的解决方案，那就是使用集合(sets)，你直接这样做：
some_list = ['a', 'b', 'c', 'b', 'd', 'm', 'n', 'n']
duplicates = set([x for x in some_list if some_list.count(x) > 1])
print(duplicates)
# 输出: set(['b', 'n'])
# 集合还有一些其它方法，下面我们介绍其中一部分。
# =========交集=========
# 你可以对比两个集合的交集（两个集合中都有的数据），如下：
valid = set(['yellow', 'red', 'blue', 'green', 'black'])
input_set = set(['red', 'brown'])
print(input_set.intersection(valid))
# 输出: set(['red'])
# =========差集===========
# 你可以用差集(difference)找出无效的数据，相当于用一个集合减去另一个集合的数据，例如：
valid = set(['yellow', 'red', 'blue', 'green', 'black'])
input_set = set(['red', 'brown'])
print(input_set.difference(valid))
# 输出: set(['brown'])
# 你也可以用符号来创建集合，如：
a_set = {'red', 'blue', 'green'}
print(type(a_set))
# 输出: <type 'set'>ZIP
keys = ['a', 'b', 'c']
valus = [1, 2, 3]
zippend = dict(zip(keys, valus))
print(zippend)
# {'a': 1, 'b': 2, 'c': 3}