Python Basics 3-iterators | Slice

There are a lot of python-specific things, very interesting, previously only contact C, C + +, Java, Javascript, did not expect to play like this

#------------------Slice--------------------##slice slices to cut out another array from an arrayLi = List (range (10))Print(LI)#[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]#[Start, End, Step] | | (start-end) to be consistent with the sign of stepPrint(Li[2:5])#[2, 3, 4]Print(Li[:4])#[0, 1, 2, 3]Print(li[5:])#[5, 6, 7, 8, 9]Print(Li[0:20:3])#[0, 3, 6, 9]#How about minusPrint(Li[5:-2])#[5, 6, 7]Print(Li[9:0:-1])#[9, 8, 7, 6, 5, 4, 3, 2, 1]Print(Li[9:0:1])# []Print(Li[9::-1])#[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]Print(Li[::-2])#[9, 7, 5, 3, 1]#a new ObjectPrint(LI) re_li= Li[::-1]#[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]Print(Re_li)#------------------Comprehension--------------------##Comprehension Deduction List# Simple CaseLi = [] forIinchRange (10): Li.append (i)Print(LI) Li= List (Range (10)):        Print(LI) Li= [1] * 10Print(LI)#Shallow Copyli_2d = [[0] * 3] * 3Print(li_2d) li_2d[0][0]= 100Print(li_2d)#Deep Copyli_2d = [[0] * 3 forIinchRange (3)]Print(li_2d) li_2d[0][0]= 100Print(li_2d) Li= (x forXinchRange (10))Print(Type (LI))#GeneratorPrint(LI)#Generator Object       forIinchRange (10):#Way1      Print(Next (LI)) forIinchLi#Way2      Print(i) Li= [x forXinchRange (10)]    Print(Type (LI))#ListPrint(LI)#[1, 2, 3, 4]Li= {X forXinchRange (3)}Print(Type (LI))#SetPrint(LI)#{0, 1, 2}s= {X forXinchRange (10)ifx%2==0}Print(Type (s))#SetPrint(s)#{0, 8, 2, 4, 6}s= [x%2==0 forXinchRange (10)]Print(Type (s))#ListPrint(s)#[True, False, Ture, False,ture, False, Ture, False, Ture, false]D= {x:x% 2 = = 0 forXinchRange (10)}Print(Type (d))#ListPrint(d)#{0:true, 1:false, 2:true, 3:false, 4:true, 5:false, 6:true, 7:false, 8:true, 9:false}#So ' x for x in range (Ten) ' is a comprehension#Generator The real calculation until it is used without generating many elements at once, saving memory#2.7 version of a one-time generation of 100W numbers, in the 3.5 version is not really generate 100W digits but the next value is generatedPrint(Type (range (10)))#type#Square TableSquare_table = [] forIinchRange (50000): Square_table.append (i*i) forIinchRange (5):    Print(Square_table[i]) Square_generator= (x * x forXinchRange (50000))Print(Type (square_generator))#Generator forIinchRange (5):    Print(Next (square_generator))deffib (limit): N, a, b= 0, 0, 1 whileN <Limit:yieldb A, b= B, A +B N+ = 1PassImportTRACEBACKF= FIB (5)Print(Type (f))Print(Next (f))Print(Next (f))Print(Next (f))Print(Next (f))Print(Next (f))Try:     Print(Next (f))exceptStopIteration:traceback.print_exc () forIinchFIB (5):    Print(i)#iterable Iterator#Iterative and iterator-like concepts can be iterated to indicate that a for loop can be used, whereas iterators are used to continuously return the next value using next (), using lazy computing#The generator must be an iterator using a build one to see the fib example below fromCollectionsImportiterable fromCollectionsImportIteratorPrint(Isinstance ([iterable])#TruePrint(Isinstance ({}, iterable))#TruePrint(Isinstance (123, iterable))#FalsePrint(Isinstance ('ABC', iterable))#TruePrint(Isinstance ([1, 2, 3], Iterator))#Falseg= (x * x forXinchRange (10))Print(Type (g))#<type ' generator ' >Print(Isinstance (g, iterable))#TruePrint(Isinstance (g, Iterator))#True forIinchg:Print(i)deffib (limit): N, a, b= 0, 0, 1 whileN <Limit:yieldb A, b= B, A +B N+ = 1PassF= FIB (5)Print(Type (f))Print(Isinstance (F, iterable))#TruePrint(Isinstance (F, Iterator))#True forIinchF:Print(i)

Python Basics 3-iterators | Slice