Reading notes-The second edition of the Basic Python Tutorial-2nd Chapter list and tuples

Chapter II List and tuples

2.1 Overview of the sequence

Sequence: Each element is assigned an ordinal

6 kinds: list, tuple, string, Unicode string, buffer object, Xrange object

Sequences can be nested sequences

Python container concepts: sequences, dictionaries, collections

2.2 Operation of a general-purpose sequence

index, Shard, add, multiply, belong, length, maximum, minimum, iteration

2.2.1 Index

>>> greeting= ' Hello '

>>> Greeting[0]

H

>>> Greeting[-1]

' O '

>>> ' Hello ' [1]

E

2.2.2 Shards

>>> numbers=[1,2,3,4,5,6,7,8]

>>> Numbers[3:6] #第一个元素包含, the second element does not contain a

[4, 5, 6]

>>> Numbers[0:1]

[1]

1. Elegant shortcuts

>>> numbers=[1,2,3,4,5,6,7,8,9,10]

>>> Numbers[7:10]

[8, 9, 10]

>>> Numbers[-3:-1] #左边的元素一定要比右边的元素早出现

[8, 9]

>>> numbers[-3:]

[8, 9, 10]

>>> Numbers[:3]

[1, 2, 3]

>>> numbers[:]

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

2. Longer stride length

>>> Numbers[0:10:1]

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

>>> Numbers[0:10:2]

[1, 3, 5, 7, 9]

>>> Numbers[::4]

[1, 5, 9]

Step is negative

>>> Numbers[8:3:-1]

[9, 8, 7, 6, 5]

>>> Numbers[10:0:-2]

[10, 8, 6, 4, 2]

>>> Numbers[0:10:-2]

[]

>>> Numbers[::-2]

[10, 8, 6, 4, 2]

>>> Numbers[5::-2]

[6, 4, 2]

>>> Numbers[:5:-2]

[10, 8]

>>>

2.2.3 Sequence Addition

>>> [1,2,3]+[4,5,6]

[1, 2, 3, 4, 5, 6]

>>> ' Hello. ' + ' world '

' Hello. World

>>> ' Hello. ' +[1,2,3]

Traceback (most recent):

File "<stdin>", line 1, in <module>

Typeerror:cannot concatenate ' str ' and ' list ' objects

only sequences of the same type can be connected

2.2.4 Multiplication

>>> ' python '

' Pythonpythonpythonpythonpython '

>>> [42]*2

[42, 42]

None, empty list, and initialization

>>> sequence=[none]*10

>>> sequence

[None, None, none, none, none, none, none, none, none, none]

2.2.5 Membership

>>> users = [' Mlh ', ' foo ', ' Bar ']

>>> raw_input (' Enter your user name: ') in users

Enter your user Name:mlh

True

#字符串判断成员是, the detection is a character, as long as the character satisfies

>>> subject= ' $$$ Get rich now!!! $$$ '

>>> ' $$$ ' in subject

True

>>> ' $$ ' in subject

True

>>> ' $ ' in subject

True

>>> ' $ $ ' in subject

False

>>> database = [' alert ', ' 1234 '],[' Jones ', ' 9845 ']

>>> if [' Alert ', ' 1234 '] in Database:print ' Access granted '

...

Access granted

2.2.5 length, min value, maximum value

>>> numbers=[100,34,478]

>>> Len (Numbers)

3

>>> Max (Numbers)

478

>>> min (Numbers)

34

>>> Max (2,3)

3

>>> min (9,3,2,5)

2

2.3 List: Python's drudgery

The list is different from the tuple and the string: The list is mutable

2.3.1 List Function List function applies to all types of sequences, not just strings

>>> list (' Hello ')

[' H ', ' e ', ' l ', ' l ', ' O ']

2.3.2 Basic List Operations

Ways to change the list:

1, change the list: element assignment, cannot assign a value to an element that does not exist in a position

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

>>> x[1]=2

>>> x

[1, 2, 1]

2, delete the element, in addition to delete the list, you can also delete the dictionary or other variables

>>> del X[1]

>>> x

[1, 1]

3, The Shard assignment, you can add the step length, the step can also be negative

>>> name=list (' Perl ')

>>> Name

[' P ', ' e ', ' r ', ' L ']

>>> name[2:]=list (' ar ')

>>> Name

[' P ', ' e ', ' a ', ' R ']

Application: can be replaced with unequal length

>>> name=list (' Perl ')

>>> name[1:]=list (' Ython ')

>>> Name

[' P ', ' y ', ' t ', ' h ', ' o ', ' n ']

New values can be inserted in one place

>>> numbers=[1,5]

>>> numbers[1:1]=[2,3,4]

>>> numbers

[1, 2, 3, 4, 5]

Can be used to delete elements

>>> numbers[1:4]=[]

>>> numbers

[1, 5]

Equivalent to: Del Numbers[1:4]

2.3.3 List Method

Method invocation: Object. Method (Parameter)

1, append does not return the value , the change is the original list

>>> lst=[1,2,3]

>>> Lst.append (4)

>>> LST

[1, 2, 3, 4]

2. Number of count statistics elements appearing in the list

>>> [' To ', ' is ', ' or ', ' not ', ' to ', ' is '].count (' to ')

2

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

>>> X.count (1)

2

>>> X.count ([up])

1

3. Extend can 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]

>>> a=[1,2,3]

>>> b=[4,5,6]

>>> a+b

[1, 2, 3, 4, 5, 6]

>>> A

[1, 2, 3]

>>> a=a+b #并没有修改原来的列表

>>> A

[1, 2, 3, 4, 5, 6]

Use shard Copy to achieve the same effect, but with poor likelihood

>>> a=[1,2,3]

>>> b=[4,5,6]

>>> A[len (a):]=b

>>> A

[1, 2, 3, 4, 5, 6]

4. Index

The index method is used to find the indexed position of the first occurrence of a value from a list

>>> knights=[' We ', ' is ', ' the ', ' knights ', ' who ', ' say ', ' ni ', ' Who ']

>>> Knights.index (' Who ')

4

>>> Knights[4]

' Who '

>>> knights.index (' Jack ')

Traceback (most recent):

File "<stdin>", line 1, in <module>

ValueError:list.index (x): X not in List

5. Insert

The Insert method is used to insert the object into the list

>>> numbers=[1,2,3,5,6,7]

>>> Numbers.insert (3, ' four ')

>>> numbers

[1, 2, 3, ' Four ', 5, 6, 7]

Use shard assignment, but can read poor

>>> numbers=[1,2,3,5,6,7]

>>> numbers[3:3]=[' four '

>>> numbers

[1, 2, 3, ' Four ', 5, 6, 7]

6. Pop

The Pop method removes the specified element from the list (the last one by default) and returns the value of the element

>>> x=[1,2,3]

>>> X.pop ()

3

>>> x

[1, 2]

>>> X.pop (0)

1

>>> x

[2]

Last-in-first-out data structure: stack

Append () +pop ()

FIFO Data structure: queue

Insert (0,...) +pop () always add to the front

>>> x=[1,2,3]

>>> X.append (X.pop ())

>>> x

[1, 2, 3]

7. Remove does not return a value removes the first occurrence in the list

>>> x=[' to ', ' being ', ' or ', ' not ', ' to ', ' being ']

>>> x.remove (' be ')

>>> x

[' to ', ' or ', ' no ', ' to ', ' being ']

>>> x.remove (' Bee ')

Traceback (most recent):

File "<stdin>", line 1, in <module>

ValueError:list.remove (x): X not in List

8, reverse not return value change the original list, reverse the original list

>>> x=[1,2,3]

>>> X.reverse ()

>>> x

[3, 2, 1]

>>> x=[1,2,3]

>>> list (reversed (x))

[3, 2, 1]

>>> Reversed (x)

<listreverseiterator Object at 0x7ffb167aaed0>

9. Sort has no return value

The sort method is used to sort the list at the original location, changing the original list

>>> x=[4,6,2,1,7,9]

>>> X.sort ()

>>> x

[1, 2, 4, 6, 7, 9]

The user needs to arrange a copy of the order, do not need to change the original list

The right approach:

>>> x=[4,6,2,1,7,9]

>>> y=x[:]

>>> Y.sort ()

>>> y

[1, 2, 4, 6, 7, 9]

>>> x

[4, 6, 2, 1, 7, 9]

>>> x=[4,6,2,1,7,9]

>>> y=sorted (x)

>>> y

[1, 2, 4, 6, 7, 9]

>>> x

[4, 6, 2, 1, 7, 9]

The wrong approach:

>>> x=[4,6,2,1,7,9]

>>> y=x

>>> Y.sort ()

>>> x

[1, 2, 4, 6, 7, 9]

>>> y

[1, 2, 4, 6, 7, 9]

10. Advanced Sorting

>>> CMP (+)

-1

>>> CMP (2,1)

1

>>> CMP (+)

0

>>> numbers=[5,2,9,7]

>>> Numbers.sort (CMP)

>>> numbers

[2, 5, 7, 9]

>>> x=[4,6,2,1,7

Specify a sorted key

>>> x=[' aardvark ', ' abalone ', ' Acme ', ' Add ', ' aerate ']

>>> X.sort (Key=len)

>>> x

[' Add ', ' Acme ', ' aerate ', ' abalone ', ' aardvark ']

Specify reverse Sort

>>> x=[4,6,2,1,7,9]

>>> X.sort (reverse=true)

>>> x

[9, 7, 6, 4, 2, 1]

2.4: Tuples: Immutable sequences

>>>

(1, 2, 3)

>>> (a)

(1, 2, 3)

>>> ()

()

How do you implement a tuple of values? You must add a reading number

>>> (41)

41

>>> (41,)

(41,)

>>> 41

41

>>> 41,

(41,)

>>> (42)

126

>>> (40+2,)

(42, 42, 42)

2.4:tuple elements

Converting a sequence to a tuple

>>> tuple ([+])

(1, 2, 3)

>>> tuple (' abc ')

(' A ', ' B ', ' C ')

>>> tuple ((+))

(1, 2, 3)

2.4.2 operation of Primitive tuples

Creating tuples

>>> x=1,2,3

>>> X[1]

2

accessing tuples

>>> X[0:2]

(1, 2)

2.4. What is the meaning of the 3-tuple

1, tuples can be used as keys in the map-and the list is not

2, tuple as a number of intrinsic functions and the return value of the method exists

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Reading notes-The second edition of the Basic Python Tutorial-2nd Chapter list and tuples