2015/8/30 Python Basics (4): Sequence operators

A sequence is a type that is ordered by a member and can be accessed by an subscript offset. Python sequences include: strings, lists, and tuples.
Each element of a sequence can be given an offset, and multiple elements are obtained by slicing the operation. The subscript offset is counted from 0 to the total-1 end.

Sequence type operator
These operators are applicable to all sequence types.

Sequence operator	Role
Seq[ind]	Get the element labeled IND
SEQ[IND1:IND2]	Gets the set of elements from Ind1 to Ind2
SEQ * Expr	Sequence repeats expr times
SEQ1 + SEQ2	Connecting sequences seq1 and SEQ2
obj in seq	Determine if the obj element is in seq
Obj not in seq	Determines whether the obj element is no longer in SEQ

Seq[ind] has the following code

>>> LST = [1,2,3,4,5,6]>>> exp ="abcdef">>> tub = ("Apple","Orange","Banana","Watermelon")>>>PrintLST[2]#the element labeled 2 in the Print List3>>>PrintEXP[0]#three sequences are used in the same waya>>>PrintTub[3]watermelon>>>PrintLST[-1]#negative index to end as the starting point6>>>PrintLST[6]#index cannot exceed sequence lengthTraceback (most recent): File"<pyshell#7>", Line 1,inch<module>PrintLST[6]#index cannot exceed sequence lengthIndexerror:list Index out of range>>>Print[1,2,3,4,5,6] [0]#you can not use the sequence assignment directly1>>>Print 'ABCDE'[0]#you can not use the sequence assignment directlyA

There are several usage scenarios that cover the seq[ind]. The positive index offset number is 0 to (the total number of elements-1), starting from the first element index, negative index offset is 1 to negative total number of elements, starting from the tail element index.

However, this indexing method can only index one element, and multiple element indexes use

Sequence[start_index:end_index (: Step)]

Have the following code

>>> LST = [1, 2, 3, 4, 5, 6]>>>Printlst[:]#omit two coordinates from start to finish[1, 2, 3, 4, 5, 6]>>>PrintLst[3:]#omit End coordinate[4, 5, 6]>>>PrintLst[:5]#Omit start coordinates[1, 2, 3, 4, 5]>>>PrintLST[::2]#step is 2, take one[1, 3, 5]>>>PrintLST[::-1]#Reverse Sequence[6, 5, 4, 3, 2, 1]>>>PrintLst[1:5:2]#from coordinates 1 to coordinates 5, take one[2, 4]>>>PrintLst[-5:-3][2, 3]>>>Printlst[-1:100][6]>>>PrintLST[-6:-4]#negative index, not negative output[1, 2]>>>PrintLst[-3:5]#when the positive and negative indexes exist, the coordinates only represent the position and the elements between the positions are intercepted.[4, 5]>>>PrintLST[:100]#index can exceed sequence length[1, 2, 3, 4, 5, 6]>>>PrintLST[-5:100]#index can exceed sequence length[2, 3, 4, 5, 6]

There is one more thing to say about slicing operations, if you use a negative index:

>>> lst = [1,2,3,4,5,6,7]>>> print lst[:-2][1, 2, 3, 4, 5]>>> print lst[:-1][1 , 2, 3, 4, 5, 6]>>> print lst[:0][]     

When a negative index is a tail coordinate, we can never intercept the last element, because 1 is the maximum value of the negative index, and if you use 0 it is considered a positive index.

In this case, we can use none to replace the 0 position

Print lst[:none][1, 2, 3, 4, 5, 6, 7]

Connection operator +

The join operator allows multiple sequences to be joined together, but only the same object can be connected. are lists, both strings or tuples

>>> Num_lst = [1,2,3,4]>>> mixup_lst = [567,'ABC', [123,'AAA']]>>> Num_lst +mixup_lst[1, 2, 3, 4, 567,'ABC', [123,'AAA']]>>> string ='abcdef'>>> Num_lst +Stringtraceback (most recent): File"<pyshell#4>", Line 1,inch<module>Num_lst+Stringtypeerror:can only concatenate list ( not "Str") to List

Repeating operator (*)

>>> mixup_lst = [567,'ABC', [123,'AAA']]>>> string ='abcdef'>>> Mixup_lst * 2[567,'ABC', [123,'AAA'], 567,'ABC', [123,'AAA']]>>> String * 3'Abcdefabcdefabcdef'>>> Mixup_lst *Mixup_lsttraceback (most recent): File"<pyshell#9>", Line 1,inch<module>Mixup_lst*Mixup_lsttypeerror:can't multiply sequence by non-int of type'List'

* After the number can only be received, representing the number of repetitions, otherwise it will be wrong

Member relationship operation in, not in

>>> mixup_list = ['a', 123,['x', 1.4,35]]>>>'a' inchmixup_listtrue>>>'x' inchMixup_listfalse>>>'x' inchMixup_list[2]true>>> string ='abcdef'>>>'a' inchstringtrue>>>'BCD' inchstringtrue>>>'Abd' inchStringfalse

These are the actions of in, which determine whether the element belongs to this sequence. The result is the opposite if you use not.

2015/8/30 Python Basics (4): Sequence operators