【文末送书】非常实用的 Python 技巧
【摘要】
别忘了查看文末送书送书哦！
函数连续调用
def add(x): class AddNum(int): def __call__(self, x): return AddNum(self.numerator + x) return AddNum(x)print add(2)(3)(5)# 10print add(2)(3)(4)(5)(6)(7)# 27#...
别忘了查看文末送书送书哦！
函数连续调用
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def add(x):
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class AddNum(int):
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def __call__(self, x):
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return AddNum(self.numerator + x)
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return AddNum(x)
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print add(2)(3)(5)
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# 10
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print add(2)(3)(4)(5)(6)(7)
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# 27
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# javascript 版
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var add = function(x){
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var addNum = function(x){
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return add(addNum + x);
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};
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addNum.toString = function(){
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return x;
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}
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return addNum;
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}
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add(2)(3)(5)//10
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add(2)(3)(4)(5)(6)(7)//27
默认值陷阱
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>>> def evil(v=[]):
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... v.append(1)
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... print v
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...
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>>> evil()
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[1]
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>>> evil()
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[1, 1]
读写csv文件
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import csv
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with open('data.csv', 'rb') as f:
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reader = csv.reader(f)
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for row in reader:
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print row
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# 向csv文件写入
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import csv
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with open( 'data.csv', 'wb') as f:
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writer = csv.writer(f)
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writer.writerow(['name', 'address', 'age']) # 单行写入
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data = [
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( 'xiaoming ','china','10'),
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( 'Lily', 'USA', '12')]
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writer.writerows(data) # 多行写入
数制转换
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>>> int('1000', 2)
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8
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>>> int('A', 16)
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10
格式化 json
echo'{"k": "v"}' | python-m json.tool
list 扁平化
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list_ = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
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[k for i in list_ for k in i] #[1, 2, 3, 4, 5, 6, 7, 8, 9]
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import numpy as np
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print np.r_[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
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import itertools
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print list(itertools.chain(*[[1, 2, 3], [4, 5, 6], [7, 8, 9]]))
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sum(list_, [])
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flatten = lambda x: [y for l in x for y in flatten(l)] if type(x) is list else [x]
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flatten(list_)
list 合并
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>>> a = [1, 3, 5, 7, 9]
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>>> b = [2, 3, 4, 5, 6]
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>>> c = [5, 6, 7, 8, 9]
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>>> list(set().union(a, b, c))
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[1, 2, 3, 4, 5, 6, 7, 8, 9]
出现次数最多的 2 个字母
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from collections import Counter
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c = Counter('hello world')
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print(c.most_common(2)) #[('l', 3), ('o', 2)]
谨慎使用
eval("__import__('os').system('rm -rf /')", {})
置换矩阵
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matrix = [[1, 2, 3],[4, 5, 6]]
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res = zip( *matrix ) # res = [(1, 4), (2, 5), (3, 6)]
列表推导
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[item**2 for item in lst if item % 2]
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map(lambda item: item ** 2, filter(lambda item: item % 2, lst))
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>>> list(map(str, [1, 2, 3, 4, 5, 6, 7, 8, 9]))
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['1', '2', '3', '4', '5', '6', '7', '8', '9']
排列组合
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>>> for p in itertools.permutations([1, 2, 3, 4]):
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... print ''.join(str(x) for x in p)
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...
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1234
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1243
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1324
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1342
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1423
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1432
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2134
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2143
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2314
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2341
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2413
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2431
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3124
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3142
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3214
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3241
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3412
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3421
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4123
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4132
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4213
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4231
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4312
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4321
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>>> for c in itertools.combinations([1, 2, 3, 4, 5], 3):
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... print ''.join(str(x) for x in c)
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...
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123
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124
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125
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134
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135
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145
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234
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235
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245
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345
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>>> for c in itertools.combinations_with_replacement([1, 2, 3], 2):
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... print ''.join(str(x) for x in c)
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...
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11
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12
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13
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22
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23
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33
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>>> for p in itertools.product([1, 2, 3], [4, 5]):
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(1, 4)
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(1, 5)
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(2, 4)
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(2, 5)
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(3, 4)
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(3, 5)
默认字典
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>>> m = dict()
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>>> m['a']
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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KeyError: 'a'
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>>>
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>>> m = collections.defaultdict(int)
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>>> m['a']
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0
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>>> m['b']
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0
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>>> m = collections.defaultdict(str)
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>>> m['a']
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''
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>>> m['b'] += 'a'
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>>> m['b']
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'a'
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>>> m = collections.defaultdict(lambda: '[default value]')
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>>> m['a']
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'[default value]'
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>>> m['b']
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'[default value]'
反转字典
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>>> m = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
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>>> m
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{'d': 4, 'a': 1, 'b': 2, 'c': 3}
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>>> {v: k for k, v in m.items()}
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{1: 'a', 2: 'b', 3: 'c', 4: 'd'}
更多
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https://www.zhihu.com/question/27376156
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stackoverflow.com/questions/101268/hidden-features-of-python
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https://zhuanlan.zhihu.com/p/22909144
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https://www.zhihu.com/question/29995881
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本次送书规则
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《Python网络爬虫开发》
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（点击查看详情）
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本次送书5本
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1、公众号回复：送书 参与活动
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2、扫一扫下方的二维码参与送书
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文章来源: blog.csdn.net，作者：敲代码的灰太狼，版权归原作者所有，如需转载，请联系作者。
原文链接：blog.csdn.net/tongtongjing1765/article/details/108114403
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