Python base 03 Sequence

Sequence sequence

A sequence sequence is a set of sequential elements

(strictly speaking, It is a collection of objects, but given the concept of not introducing objects, temporarily say elements)

A sequence can contain one or more elements , or it can have no elements

The basic data types we mentioned earlier can be used as elements of a sequence. The element can also be another sequence, as well as other objects we later Have.

There are two types of sequences: tuple ( fixed value table : Also called tuple ), and list ( list )

S1 = (2,1.3, ' Love ', 5.6,9,false)　 #是一个tuple
s2 = [true,5, ' Smile '] #是一个list

Print (s1,type (s1))

([True, 5, ' Smile '], <type ' tuple ' >)

Print (s2,type (s2))

([True, 5, ' Smile '], <type ' list ' >)

The main difference between a tuple and a list is that once established,each element of a tuple cannot be changed, and the elements of the list can be changed Again.

A sequence as an element of another sequence

S3 = [1,[3,4,5]]

Empty sequence

S4 = []

References to elements

The subscript of the sequence element starts with 0 :

Print (s1[01])

1.3

Print (s2[2])

Smile

Print (s1[1][2])

V

Because the list element is notconsistent, you can assign a value to the list

s2[1] = 3.0

Print (s2)

Above output

3.0

If you do this to a tuple, you get an error message.

so, you can see that the reference to the sequence is implemented by s[int] , and int is Subscript.

Other citation methods (slices)

Range reference: basic style [ lower limit: Upper limit: step length ]

Print (s1[:5]) #从开始到下标4 (the Elements of subscript 5 are not included)　　

(2, 1.3, ' Love ', 5.6, 9)

Print (s1[2:]) #从下标2到最后　

(' Love ', 5.6, 9, False)

print (s1[0:5:2])　 #从下标0到下标4 (not included in subscript 5), each 2 element ()

(2, ' Love ', 9)

Print (s1[2:0:-1]) #从下标2到下标1

(' Love ', 1.3)

As can be seen in the scope reference, if the upper limit is indicated, then the upper limit itself is not included .

Trailing element reference

Print (s1[-1]) #序列last element　　

Print (s1[-3])　 #序列倒数第三个元素　

string is a tuple

Strings are special tuples, so you can perform related operations on Tuples.

str = ' abcdef '

Print (str (2:4))

' CD '

Summarize

Tuple element immutable, list element variable

A reference to a sequence s[2],s[1:8:2]

A string is a tuple

Python base 03 Sequence