l临沂建设工程信息网站,北京首钢建设有限公司网站,国外室内设计网站大全网站,权威的网站制作1、原地交换两个数字 1 2 3 4 x, y 10, 20 print(x, y) y, x x, y print(x, y) 10 20
20 10 2、链状比较操作符 1 2 3 n 10 print(1 n 20) print(1 n 9) True
False 3、使用三元操作符来实现条件赋值 [表达式为真的返回值] if [表达式] else [表达式… 1、原地交换两个数字 1 2 3 4 x, y 10, 20 print(x, y) y, x x, y print(x, y) 10 20
20 10 2、链状比较操作符 1 2 3 n 10 print(1 n 20) print(1 n 9) True
False 3、使用三元操作符来实现条件赋值 [表达式为真的返回值] if [表达式] else [表达式为假的返回值] 1 2 3 y 20 x 9 if (y 10) else 8 print(x)
8 # 找abc中最小的数 1 2 3 4 5 6 def small(a, b, c): return a if ab and ac else (b if ba and bc else c) print(small(1, 0, 1)) print(small(1, 2, 2)) print(small(2, 2, 3)) print(small(5, 4, 3))
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3 1 2 3 # 列表推导 x [m**2 if m10 else m**4 for m in range(50)] print(x)
[0, 1, 16, 81, 256, 625, 1296, 2401, 4096, 6561, 10000, 121, 144, 169, 196, 225, 256, 289, 324, 361, 400, 441, 484, 529, 576, 625, 676, 729, 784, 841, 900, 961, 1024, 1089, 1156, 1225, 1296, 1369, 1444, 1521, 1600, 1681, 1764, 1849, 1936, 2025, 2116, 2209, 2304, 2401] 4、多行字符串 1 2 3 4 5 6 7 8 9 10 11 12 13 14 multistr select * from multi_row \ where row_id 5 print(multistr) select * from multi_row where row_id 5 multistr select * from multi_row where row_id 5 print(multistr) select * from multi_row where row_id 5 multistr (select * from multi_row where row_id 5 order by age) print(multistr) select * from multi_rowwhere row_id 5order by age 5、存储列表元素到新的变量 1 2 3 testList [1, 2, 3] x, y, z testList # 变量个数应该和列表长度严格一致 print(x, y, z)
1 2 3 6、打印引入模块的绝对路径 1 2 3 4 5 6 import threading import socket print(threading) print(socket) module threading from d:\\python351\\lib\\threading.py module socket from d:\\python351\\lib\\socket.py
7、交互环境下的“_”操作符 在python控制台不论我们测试一个表达式还是调用一个方法结果都会分配给一个临时变量“_” 8、字典/集合推导 1 2 3 4 testDic {i: i * i for i in range(10)} testSet {i * 2 for i in range(10)} print(testDic) print(testSet) {0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81} {0, 2, 4, 6, 8, 10, 12, 14, 16, 18} 9、调试脚本 用pdb模块设置断点 1 2 import pdb pdb.ste_trace() 10、开启文件分享 python允许开启一个HTTP服务器从根目录共享文件 1 python -m http.server 11、检查python中的对象 1 2 test [1, 3, 5, 7] print(dir(test)) [__add__, __class__, __contains__, __delattr__, __delitem__, __dir__, __doc__, __eq__, __format__, __ge__, __getattribute__, __getitem__, __gt__, __hash__, __iadd__, __imul__, __init__, __iter__, __le__, __len__, __lt__, __mul__, __ne__, __new__, __reduce__, __reduce_ex__, __repr__, __reversed__, __rmul__, __setattr__, __setitem__, __sizeof__, __str__, __subclasshook__, append, clear, copy, count, extend, index, insert, pop, remove, reverse, sort] 1 2 test range(10) print(dir(test)) [__class__, __contains__, __delattr__, __dir__, __doc__, __eq__, __format__, __ge__, __getattribute__, __getitem__, __gt__, __hash__, __init__, __iter__, __le__, __len__, __lt__, __ne__, __new__, __reduce__, __reduce_ex__, __repr__, __reversed__, __setattr__, __sizeof__, __str__, __subclasshook__, count, index, start, step, stop] 12、简化if语句 1 2 3 4 # use following way to verify multi values if m in [1, 2, 3, 4]: # do not use following way if m1 or m2 or m3 or m4:
13、运行时检测python版本 1 2 3 4 import sys if not hasattr(sys, hexversion) or sys.version_info ! (2, 7): print(sorry, you are not running on python 2.7) print(current python version:, sys.version)
sorry, you are not running on python 2.7 current python version: 3.5.1 (v3.5.1:37a07cee5969, Dec 6 2015, 01:54:25) [MSC v.1900 64 bit (AMD64)] 14、组合多个字符串 1 2 3 test [I, Like, Python] print(test) print(.join(test)) [I, Like, Python] ILikePython 15、四种翻转字符串、列表的方式 5
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1 16、用枚举在循环中找到索引 1 2 3 test [10, 20, 30] for i, value in enumerate(test): print(i, :, value)
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2 : 30 17、定义枚举量 1 2 3 4 5 6 class shapes: circle, square, triangle, quadrangle range(4) print(shapes.circle) print(shapes.square) print(shapes.triangle) print(shapes.quadrangle)
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3 18、从方法中返回多个值 1 2 3 4 def x(): return 1, 2, 3, 4 a, b, c, d x() print(a, b, c, d) 1 2 3 4 19、使用*运算符unpack函数参数 1 2 3 4 5 6 7 def test(x, y, z): print(x, y, z) testDic {x:1, y:2, z:3} testList [10, 20, 30] test(*testDic) test(**testDic) test(*testList)
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10 20 30 20、用字典来存储表达式 1 2 3 4 5 6 stdcalc { sum: lambda x, y: x y, subtract: lambda x, y: x - y } print(stdcalc[sum](9, 3)) print(stdcalc[subtract](9, 3))
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6 21、计算任何数的阶乘 1 2 3 import functools result (lambda k: functools.reduce(int.__mul__, range(1, k1), 1))(3) print(result)
6 22、找到列表中出现次数最多的数 1 2 test [1, 2, 3, 4, 2, 2, 3, 1, 4, 4, 4, 4] print(max(set(test), keytest.count))
4 23、重置递归限制 python限制递归次数到1000可以用下面方法重置 1 2 3 4 5 import sys x 1200 print(sys.getrecursionlimit()) sys.setrecursionlimit(x) print(sys.getrecursionlimit()) 1000 1200 24、检查一个对象的内存使用 1 2 3 import sys x 1 print(sys.getsizeof(x)) # python3.5中一个32比特的整数占用28字节 28 25、使用slots减少内存开支 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 import sys # 原始类 class FileSystem(object): def __init__(self, files, folders, devices): self.files files self.folder folders self.devices devices print(sys.getsizeof(FileSystem)) # 减少内存后 class FileSystem(object): __slots__ [files, folders, devices] def __init__(self, files, folders, devices): self.files files self.folder folders self.devices devices print(sys.getsizeof(FileSystem)) 1016 888 26、用lambda 来模仿输出方法 1 2 3 import sys lprint lambda *args: sys.stdout.write( .join(map(str, args))) lprint(python, tips, 1000, 1001) python tips 1000 1001 27、从两个相关序列构建一个字典 1 2 3 t1 (1, 2, 3) t2 (10, 20, 30) print(dict(zip(t1, t2))) {1: 10, 2: 20, 3: 30} 28、搜索字符串的多个前后缀 1 2 print(http://localhost:8888/notebooks/Untitled6.ipynb.startswith((http://, https://))) print(http://localhost:8888/notebooks/Untitled6.ipynb.endswith((.ipynb, .py)))
True True 29、不使用循环构造一个列表 1 2 3 4 import itertools import numpy as np test [[-1, -2], [30, 40], [25, 35]] print(list(itertools.chain.from_iterable(test)))
[-1, -2, 30, 40, 25, 35] 30、实现switch-case语句 1 2 3 4 5 def xswitch(x): return xswitch._system_dict.get(x, None) xswitch._system_dict {files:10, folders:5, devices:2} print(xswitch(default)) print(xswitch(devices))
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