python-List Builder

List generation: Use Python's built-in, very simple, but powerful list comprehensions to create a list of generated

Some examples:

#生成list原始方法
>>> l=list (range) >>> print (L) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 , 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77 , Bayi, 94,------------------------- 1,100): L.append (x*x) >>> print (L) [1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225, 256, 289, 324, 36  1, 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, 2500, 2601, 2704, 2809, 2916, 3025, 3136, 3249, 3364, 3481, 3600, 3721, 3 844, 3969, 4096, 4225, 4356, 4489, 4624, 4761, 4900, 5041, 5184, 5329, 5476, 5625, 5776, 5929, 6084, 6241, 6400, 6561, 672 4, 6889, 7056, 7225, 7396, 7569, 7744, 7921, 8100, 8281, 8464, 8649, 8836, 9025, 9216, 9409, 9604, 9801] 
#生成式生成comprehensions, but with syntax restrictions, add [], or report a syntax error
>>> x * x for x in range (1,11): Syntaxerror:invalid syntax
#x *x is a build condition, which is to take the square root >>> [x * x for x in range (1,11)][1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

#生成条件求平方根, but the list can be added if the even square root is read out >>> [x*x for x in range (1,11) if x%2 ==0][4, 16, 36, 64, 100]

#2个for不同参数取值, each match, this test is not commonly used >>> [m+n for M in ' ABC ' for n ' dzg ' [' Ad ', ' Az ', ' Ag ', ' Bd ', ' Bz ', ' Bg ', ' Cd ', ' Cz ', ' Cg ']

#求出系统中目录带. All catalog Collections >>> Import os>>> [D for D in Os.listdir ('. ')] [' DLLs ', ' Doc ', ' include ', ' Lib ', ' Libs ', ' LICENSE.txt ', ' NEWS.txt ', ' python.exe ', ' python3.dll ', ' python36.dll ', ' Pythonw.exe ', ' Scripts ', ' tcl ', ' Tools ', ' Vcruntime140.dll '

#当然也可以生成dict, this is the original dict>>> d={' x ': ' A ', ' y ': ' B ', ' z ': ' C '}>>> for K,v in D.items ():p rint (k, ' = ', v) x = Ay = Bz = C

#利用生成器来打印循环出key,value>>> [k + ' = ' +v for k,v in D.items () [' X=a ', ' y=b ', ' z=c ']

#在列表生成器中加入对字符串的处理条件 >>> l=[' hello ', ' world ', ' IBM ', ' Apple ']>>> [S.lower () for s in l][' hello ', ' world ' , ' IBM ', ' Apple ']>>> [S[0:1].upper () for S-l][' H ', ' W ', ' I ', ' A ']>>> [S[0:].upper () for S in L] #从0位开 Start with all caps [' Hello ', ' World ', ' IBM ', ' APPLE ']>>> [S.capitalize () for S ' in L] #第一个字母大写其它小写 [' Hello ', ' World ', ' IBM ', ' Ap Ple ']

　

This is needed when, if not remember can Baidu query. There is no good way. Use more, also remember familiar. But you know it has this function

Here's a final question:

#L =[' HEllo ', ' World ', ' apple ', None]

#期待输出: [' Hello ', ' world ', ' Apple ']

>>> l=[' HEllo ', ' World ', ' apple ',none]>>> l1=[]>>> [i-I in L if Isinstance (i,str)] [' HEllo ', ' World ', ' apple ']>>>-i in L:if isinstance (I,STR): L1.append (i) >>> [X.lower () for x in l1][' he Llo ', ' World ', ' Apple '

　　

python-List Builder