Python Basics review-1-2 data types-STR, list, tuple, dict

Data type number

引号：    123  数值    ‘123‘ 字符串    整数：ini long   范围：（-2**31 - 2**31）        num = 123    长整型 long  (L)        num = 123L浮点型：float复数型：

Sequence

String, list, tuple all belong to sequence

The two main features of a sequence are index operations and slicing operations

• Index operations can fetch a specific item from the sequence
• Slice operations can get a slice from the sequence, which is part of the sequence

Basic operation of the sequence

• Len (): Find the length of the sequence
• • : Connect two sequences
• • : Repeating sequence elements
• In: Determines whether the element is in sequence
• Max (); Returns the maximum value
• Min (); Returns the minimum value
• CMP (x, y): compare two sequences for equality

String str

字符串：    str = ‘this is a string‘      单引号    str = "this is a strting"     双引号    str = ‘‘‘this is a string‘‘‘  三引号    str = """ this is a strtng """        单双引号在python下没有区别    三重引号 除了能定义字符串(可包含换行符)  还可以用作注释

Slice

Applies to all sequences
```
In [9]: a = ' abcdef '

In [ten]: A[0:2]
OUT[10]: ' AB '
Remove the label 0 to 2 subscript 2 does not display
In [all]: A[:2]
OUT[11]: ' AB '
Remove the label 0 to 2 subscript 2 does not display
In []: A[:-1]
OUT[12]: ' ABCDE '
Remove the mark 0 to the bottom 1th subscript to the bottom of the 1th one does not show
In []: A[::2]
OUT[13]: ' Ace '
Step is 2, which means to remove the mark 0, 2, 4, 6
In []: A[-3:-1]
OUT[14]: ' De '
From the bottom 3rd to the bottom 1th, the countdown 1th does not show
In []: A[-1:-4:-1]
OUT[15]: ' Fed '
Reverse slice, from the penultimate to the 4th to the bottom, the bottom 4th does not show
in [+]: a[-1:-4:-2]
OUT[16]: ' FD '
Reverse slicing, from the penultimate to the 4th to the bottom, with a step of 2
```

Summarize:
A = "abcdef"

a[A:B:C]A:切片开始的下标，包含B:切片结束的下标，不包含C:正数时表示步长  负数时表示进行反向切片及步长  

Tuple tuble

• Tuples are immutable like strings
• Tuples can store a series of values
• Tuples are usually orientating when a user-defined function can safely take a set of values, that is, the value of the tuple being used does not change

Define tuples;

t = tuble () defines a tuple of multiple elements with the number of cells, the element can be a number, a string, a list, a tuple
t = (1,) when there is only one element, one must be added, the number is not added, the value is assigned to a number
T = () defines an empty tuple

Splitting of tuples:
t = (1, 2, 3)
A, b, C = T assigns the values of tuples 1, 2, and 3 to A, B, and C in turn

Method:

Count () Number of statistics elements in tuples
Index () returns elements in the first occurrence of an element in the subscript

Lists List

• A list is a data structure that processes a set of ordered items, that is, a sequence of items that can be stored in a list
• Lists are mutable types of data
• Create a list

List1 = [] Create an empty list

List2 = List () using the list method

List3 = [' A ', 1, [' A ', 1]]

Method:

• Append () Append

  L.append (object)--Append object to end

• Del List[n] Delete an element based on the subscript

• Remove () Removes the first occurrence of the list in the element

  L.remove (value)--Remove first occurrence of value.

• Insert () inserts an element before a field index

  L.insert (Index, object)--Insert object before index

• Sort () to list remember order

  L.sort (Cmp=none, Key=none, Reverse=false)--stable sort in place;

  CMP (x, y)-1, 0, 1

• Reverse () reversal

  L.reverse ()--Reverse *in place*

• Pop () deletes and returns the element value of the specified subscript, without specifying the default deletion of the last

  L.pop ([index]), item-Remove and return item at index (default last).

• Extend () extending the list by appending iteration elements
  Extend list by appending elements from the iterable

Dictionary

• Dictionary is the only type of mapping in Python (hash table)
• The Dictionary object is mutable, but the key of the dictionary must be an immutable object, and a dictionary can use different types of key values
• Create a dictionary

Dict1 = {} using {} to create an empty dictionary

Dict2 = {' name ': ' Li ', ' Age ': 10}

DICT3 = Dict ([' Name ', ' Li '), (' Age ', 10)])

Dict4 = Dict (' A ' =10, ' n ' =100)

• Method of the Dictionary:

• Keys () Get all keys

  D.keys (), List of D ' s keys

• VALUES () gets all values

• D.values (), List of D ' s values

• Get () Gets the value corresponding to the key, does not exist when the output can be specified, default is empty

  D.get (K[,d]), D[k] if k in D, else D. D defaults to None.

• Has_key () to see if key exists

  D.has_key (k)-True if D has a key k, else False

• Iitems () converted to a list of (key, value)

  D.items (), List of D ' s (key, value) pairs, as 2-tuples

• Copy () copying

  D.copy (), a shallow copy of D

• Clear () Empty dictionary

  D.clear (), None. Remove all items from D

• Pop () deletes the value of the specified key and returns value if the key does not exist to return a given value, otherwise throws a guide

  D.pop (K[,d])-V, remove specified key and return the corresponding value.
  If key is no found, D is returned if given, otherwise keyerror is raised

• Update () updates a dictionary from a dictionary or two iteration objects

  D.update ([E,]**f), None. Update D from Dict/iterable E and F.

  If E present and has A. Keys () method, Does:for k in e:d[k] = E[k]

  If E present and lacks. Keys () method, Does:for (K, v) in e:d[k] = V

  In either case, this is followed By:for k in f:d[k] = F[k]

• Fromkeys () uses a sequence to generate a dictionary with a default value of NULL, which specifies

  Dict.fromkeys (S[,v]), New dict with keys from S and values equal to V.
  V defaults to None.

Python Basics review-1-2 data types-STR, list, tuple, dict