A sequence of basic python tutorials

sequence Sequence

Sequence (sequence) is a set of sequential elements

(Strictly speaking, it is a collection of objects, but given that we have not yet introduced the concept of "object", 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 will introduce later.

There are two types of sequences: tuple (fixed value table; also translated as tuple) and List (table)

The code is as follows:

>>>S1 = (2, 1.3, ' love ', 5.6, 9,, False) # S1 is a tuple

>>>S2 = [True, 5, ' smile '] # s2 is a list

>>>print S1,type (S1)

>>>print S2,type (S2)

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

The code is as follows:

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

Empty sequence

The code is as follows:

>>>S4 = []

references to elements

The subscript of the sequence element starts with 0:

The code is as follows:

>>>print S1[0]

>>>print S2[2]

>>>print S3[1][2]

Because the elements of the list can be changed, you can assign a value to an element of list:

The code is as follows:

>>>S2[1] = 3.0

>>>print S2

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[ ], and int is subscript

Other reference methods

Range reference: Basic style [lower limit: Upper limit: Step length]

The code is as follows:

>>>print S1[:5] # from start to subscript 4 (the elements of subscript 5 are not included)

>>>print s1[2:] # from Subscript 2 to the last

>>>print S1[0:5:2] # from subscript 0 to subscript 4 (subscript 5 not included), take one element every 2 (the element labeled 0,2,4)

>>>print S1[2:0:-1] # from subscript 2 to subscript 1

As can be seen from the above, the upper limit is not included in the range reference when the upper limit is indicated.

Trailing element reference

The code is as follows:

>>>print S1[-1] # The last element of a sequence

>>>print S1[-3] # third element of sequence countdown

Similarly, if s1[0:-1], then the last element will not be referenced (again, excluding the upper bound element itself)

string is a tuple

strings are a special element, so you can perform related operations on tuples.

The code is as follows:

>>>str = ' abcdef '

>>>print Str[2:4]

Summary

Tuple element immutable, List element variable

Sequence of references s[2], S[1:8:2]

A string is a tuple

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