Common list and tuple methods and considerations for Python sequences

The sequence sequence

A sequence(sequence) is a collection of sequential objects. A sequence can contain one or more elements, or none at all.

All of the basic data types we talked about earlier can be used as objects in a sequence. An object can also be another sequence. There are two types of sequences: a list (table) and a tuple (tuple).
The main difference between a list and a tuple is that, once established, the individual elements of a tuple cannot be changed, while the individual elements of a list can be changed again.

The List

Get the number of list elements:

>>> lst=[' Update slow ','python',5.44,False]

>>> len(lst)

4

Index starts at 0 when reference access, be careful not to cross the line:

>>> lst[0]

' Update slow '

>>> lst[1]

'python'

>>> lst[2]

5.44

>>> lst[3]

False

>>> lst[4]

Traceback (most recent call last):

  File "<pyshell#30>", line 1, in <module>

    lst[4]

IndexError: list index out of range

Index with -1, get the last element directly:

>>> lst[-1]

False

>>> lst[-2]

5.44

>>> lst[-3]

'python'

>>> lst[-4]

' Update slow '

>>> lst[-5]

Traceback (most recent call last):

  File "<pyshell#35>", line 1, in <module>

    lst[-5]

IndexError: list index out of range

Since list is a mutable ordered table, you can append elements to the end of list:

>>> lst.append(' Add me in ')

>>> lst

[' Update slow ', 'python', 5.44, False, ' Add me in ']

Append more than one element at a time:

>>> lst.extend(['A','B','C'])

>>> lst

[' Update slow ', 'python', 5.44, False, ' Add me in ', 'A', 'B', 'C']

To delete the element at the end of the list, use the pop() method:

>>> lst.pop()

'C'

>>> lst

[' Update slow ', 'python', 5.44, False, ' Add me in ', 'A', 'B']

Deletes the element in the specified position, using the pop(I) method, where I is the index position:

>>> lst.pop(0)

' Update slow '

>>> lst

['python', 5.44, False, ' Add me in ', 'A']

List element replacement, can be directly assigned to the corresponding index position:

>>> lst[-1]='100'

>>> lst

['python', 5.44, False, ' Add me in ', '100']

The list element can also be another list, and the inserted list only counts as one element:

>>> lst.append(lst1)

>>> lst

['python', 5.44, False, ' Add me in ', '100', ['666', 'QWER']]

>>> len(lst)

6

A Tuple

Once a Tuple is initialized, it cannot be modified. A string is a special element, so you can perform tuple related operations.

>>> str=' It's time for bed. Good night! '

>>> print (str[:7])

 Time for bed. Good night 

The point of an immutable tuple is that code is safer because it is immutable. If you can use a tuple, use a tuple.

>>> tuple=('1','2','3')

>>> tuple[0]=6

Traceback (most recent call last):

  File "<pyshell#62>", line 1, in <module>

    tuple[0]=6

TypeError: 'tuple' object does not support item assignment

Define an empty tuple:

>>> tuple1=()

>>> tuple1

()

Note that to define a tuple with only 1 element:

>>> tuple2=(666,)

>>> tuple2

(666,)              # The correct 

>>> tuple3=(666)

>>> tuple3

666                 # Wrong, just defined 666 The number of 

Note: when a Tuple says "invariant," it means that every element of a Tuple has the same point forever.

>>> l=['CCTV-5','HI']

>>> tuple4=('UFO','HACK',l)

>>> tuple4

('UFO', 'HACK', ['CCTV-5', 'HI'])

>>> l[1]=' Let me change that '

>>> tuple4

('UFO', 'HACK', ['CCTV-5', ' Let me change that '])

So try to avoid it.

The summary

Master the common methods and considerations for lists and tuples.