Python: List functions

List function:

Converts a string into a list, for example:

>>> name = list (' hello ')
>>> name
[' H ', ' e ', ' l ', ' l ', ' O ']

List Basic functions:

1. Change list: element assignment

Using index tags

>>>x = [1, 1, 1]
>>>x[1] = 2
>>>x
[1, 2, 1]

2, delete elements

Del Statement implementation

>>>names = [' One ', ' two ', ' three ']
>>>del names[1]
>>>names
[' One ', ' three ']

3. Piecewise assignment (the first parameter is the starting position of the beginning fragment, the second is the next position of the end fragment)

Modify a sequence

>>>name = List (' Perl ')
>>>name[1:] = List (' Ython ')
>>>name
[' P ', ' y ', ', ' t ', ' h ' , ' O ', ' n ']

Insert Sequence

>>>num = [1, 5]
>>>num[1:1] = [2, 3, 4]
>>>num
[1, 2, 3, 4, 5]

Delete a sequence

>>>num = [1, 5]
>>>num[1:1] = [2, 3, 4]
>>>num
[1, 2, 3, 4, 5]

4, append function (change the original list) (can be implemented into the stack operation)

Add a new object at the end of the list

>>>num = [1, 5]
>>>num[1:1] = [2, 3, 4]
>>>num
[1, 2, 3, 4, 5]

5, Count function

Count the number of times an element appears in the list

>>>[' to ', ' being ', ' or ', ' not ', ' to ', ' being '].count (' to ')
2

>>>x = [[1, 2], 1, 1, [2, 1, [1, 2]]]
  >>>x.count (1)
2
>>>x.cout ([1, 2])
1

6, Extend function (modify the original sequence, connect the operation to produce a new sequence)

Append multiple values from another sequence at the end of the list (expand the original list with the new list)

>>>a = [1, 2, 3]
>>>b = [4, 5, 6]
>>>a.extend (b)
>>>a
[1, 2, 3, 4, 5, 6]

Using the fragment operation to achieve the above steps

>>>a = [1, 2, 3]
>>>b = [4, 5, 6]
>>>a[len (a):] = b
>>>a
[1, 2, 3, 4, 5, 6]

7, Index function

Find the index position of the first occurrence of a value from the list

>>>num = [' One ', ' two ', ' three ', ' four ', ' five ']
>>>num.index[' three ']
2

>> >NUM[2]
' three '

8. Insert function

Insert an object into a list

>>> numbers = [1, 2, 3, 5, 6, 7]
>>> Numbers.insert (3, ' four ')
>>> numbers
[1, 2, 3 , ' Four ', 5, 6, 7]

9, Pop function (can realize the stack operation)

Removes an element from the list (the default last element) and returns the value of the element

>>> x = [1, 2, 3]
>>> x.pop ()
3
>>> x
[1, 2]

>>> x.pop (0)
1
>>> x
[2]

10, remove function (and pop difference, modify the original sequence, but do not return)

Removes the first occurrence of a value in a list

>>> x = [' To ', ' is ', ' or ', ' not ', ' to ', ' is ']
>>> x.remove (' being ')
>>> x
[' to '], ' Or ', ' not ', ' to ', ' is ']

11. Reverse function

Reverse elements in a list

>>> x = [1, 2, 3]
>>> x.reverse ()
>>> x
[3, 2, 1]

12, Sort function (change the original list, but do not return)

Sort the original list

>>> x = [4, 6, 2, 3, 5, 1]
>>> x.sort ()
>>> x
[1, 2, 3, 4, 5, 6]

If you do not need to modify the original sequence (note: if x = y is used here, then X and y all point to the same list, even if the operation is just sorted for y, and X is actually sorted)

Method One: Create a replica y and sort the Y

>>> x = [4, 6, 2, 3, 5, 1]
>>> y = x[:]
>>> y.sort ()
>>> x
[4, 6, 2, 3, 5, 1]
>>> y
[1, 2, 3, 4, 5, 6]

Method Two: Use the sorted function (return a sorted copy, do not change the original sequence)

>>> x = [4, 6, 2, 3, 5, 1]
>>> y = sorted (x)
>>> y
[1, 2, 3, 4, 5, 6]
>& gt;> x
[4, 6, 2, 3, 5, 1]

Keyword ordering: key

Length (len) Sort:

>>> x = [' BB ', ' eeeee ', ' a ', ' dddd ', ' CCC ']
>>> x.sort (key = len)
>>> x
[' A ', ' BB ', ' CCC ', ' dddd ', ' eeeee ']

Keyword ordering: reverse (Simple Boolean sort, true from large to small, false from young to large)

>>> x = [4, 6, 2, 3, 5, 1]
>>> x.sort (reverse = True)
>>> x
[6, 5, 4, 3, 2, 1]
>>> y = [4, 6, 2, 3, 5, 1]
>>> y.sort (reverse = False)
>>> y
[1, 2, 3, 4, 5, 6]

13, CMP (x, y) functions (you can customize the compare (x, y) function to compare two elements)

Compare the size of two functions

>>> CMP
-1
>>> cmp (
1)
>>> cmp (
0).

With the sort function, you can customize sorting, sort (CMP)