Python basic data type (iv)-collection and operator-python3 notes

1. Collection

2. Dictionaries

3. Operator Precedence

1. Collection

Create: () set () Note: Create an empty collection with Set () Feature: element unique, unordered operation: & (Intersection)-(set)-(difference) method: S.add (x) #添加单个元素s. Update () #添加多个元素s. Remove () #移除元素s. Clear () #清空集合 # collection creation >>> SE = {<class} >>> print (Type (SE)) ' Set ' > >&    Gt;> se = {1,2,2,3} #去重, unique >>> print (SE) {1, 2, 3} >>> se = {1, ' a ', 2, ' B '} #无序      >>> SE {1, 2, ' A ', ' B '} #可hash的能放入集合 >>> hash ([up]) Traceback (most recent call last): File "<pyshell#24>", line 1, in <module> hash ([]) typeerror:unhashable type: ' List ' >>& Gt Hash ((a,2)) Traceback (most recent): File "<pyshell#25>", line 1, in <module> hash ((A , 2)) Nameerror:name ' A ' is not defined >>> hash (()) 1299869600 >>> hash (' qwe ')-91777        3703 >>> a Traceback (most recent): File ' <pyshell#28> ', line 1, in <module> A nameerror:Name ' A ' isn't defined >>> a= ' I love python ' >>> a ' I love Python ' >>> hash (a) -2061797837 >>> #定义空集合 (Factory mode definition collection) >>> SE = set () >>> print (Type (SE)) <class ' Set '    > #集合的运算 #属于 >>> a {1, 2, 3, 4, ' a '} >>> ' a ' in a True >>> ' B ' isn't in a True #延伸 >>> se={1,2,3,4} >>> se2={3,4,5,6} >>> se < se2 #包含 False > >> se <= se2 #包含 False >>> se! = se2 #不等于 True #并集 (two sets added and de-weighed) >>> se1={1,2,3 };se2={2,3,4} >>> se1|se2 {1, 2, 3, 4} #交集 (take two duplicate elements) >>> Se1&se2 {2, 3} #差集 (Previous set     Minus the repeating part of the collection Element) >>> Se1-se2 {1} >>> se2-se1 {4} #与非集 (take separate parts of the respective collection) >>> Se1^se2 {1, 4} #集合的基本方法 View collection methods: >>> dir (SE) [' __and__ ', ' __class__ ', ' __contains__ ', ' __delattr__ ', ' __dir__ ', ' __doc__ ', ' __eq__ ', ' __fOrmat__ ', ' __ge__ ', ' __getattribute__ ', ' __gt__ ', ' __hash__ ', ' __iand__ ', ' __init__ ', ' __init_subclass__ ', ' __ior__ ', ' __isub__ ', ' __iter__ ', ' __ixor__ ', ' __le__ ', ' __len__ ', ' __lt__ ', ' __ne__ ', ' __new__ ', ' __or__ ', ' __rand__ ', ' __reduce__ ' ', ' __reduce_ex__ ', ' __repr__ ', ' __ror__ ', ' __rsub__ ', ' __rxor__ ', ' __setattr__ ', ' __sizeof__ ', ' __str__ ', ' __sub__ ', ' _ _subclasshook__ ', ' __xor__ ', ' Add ', ' clear ', ' copy ', ' Difference ', ' difference_update ', ' discard ', ' intersection ', ' Intersection_update ', ' isdisjoint ', ' issubset ', ' issuperset ', ' Pop ', ' Remove ', ' symmetric_difference ', ' symmetric_ Difference_update ', ' Union ', ' Update '] #添加单个元素 (add a single element) >>> se={1,2} >>> se.add (3) &GT;&GT;&G T Print (SE) {1, 2, 3} #添加多个元素 (add multiple elements (objects that can be iterated)) >>> se.update (' 4 ') >>> print (SE) {1, 2, 3, ' 4 '} >>> se.update (' 456 ') >>> print (SE) {1, 2, 3, ' 6 ', ' 4 ', ' 5 '} #移除元素 (specify remove) >>> s   E.remove (' 5 ') >>> print (SE) {1, 2, 3, ' 6 ', ' 4 '} #随机移除 >>> Se.pop () 1 #清空集合 >>> se.clear () >>> print (SE) Set ()

2. Dictionary

Note: Is the only mapping type created in Python: {key:value} #大括号创建字典的键时要加引号dict {key=value} #括号里赋值方式, name = object, do not quote the key and value in the dictionary are separated by ': ', a pair of keys and values form an item, a key and an item Use ', ' separates the characteristics: The key is unique, the repetition will be re-assigned the unordered key must follow the Python naming rules to add and value Cidt[key]=value #key存在则修改该值, did not add the property method:. Update ({}) #在字典中添加多个项. It       EMS () #返回字典的各个项. Keys () #返回字典的键. VALUES () #返回字典的值. Get (k) #如果键k在, returns the value of K, does not exist returns None.get (K,X) #如果键k在, returns the value of the key K, returns X.pop (k) #返回并移除键k所对应的元素, does not exist, throws an exception. Pop (k,x) #返回并移除键k所对应的元素, does not exist then returns x Summary: Key is unique, so it can be a number, a string , Ganso Summary: mutable object: List Set dict immutable object: str tuple# dictionary Unique mapping type, followed by hash, must be immutable object # definition Dictionary >>> di={' W ': 123, ' l ': 456, ' x ' : 789} >>> Print (Type (DI)) <class ' dict ' > >>> di=dict (_i=123) >>> di {' _i ': 123} >>> Print (Type (DI)) <class ' dict ' > >>> di={1:123,2:234} >>> print (t    Ype (di)) <class ' dict ' > >>> di1={' e ': [123,456]} >>> type (di1) <class ' dict ' > >>> di2={' E ':(123,456)} >>> di3={' e ': ' 123 '} >>> type (di3) <class ' dict ' > #定义空字典 >>> di1=dict () >>> print (Type (DI1)) <class ' dict ' > #字典取值 (using key values) >>> Di[1] 123 >> > di[2] 234 #字典修改 >>> di[1]= ' qwe ' >>> di {1: ' Qwe ', 2:234} #添加key: Value (key exists when the key is modified) Modify otherwise Add) >>> di[3]=890 >>> di {1: ' qwe ', 2:234, 3:890} >>> di={' Q ': 1, ' W ': 2, (' Q ', ' W '): 122} >>> di {' Q ': 1, ' W ': 2, (' Q ', ' W '): 122} #清空字典 >>> di.clear () >>> print (d i) {} #查看字典的属性方法 >>> dir (di) [' __class__ ', ' __contains__ ', ' __delattr__ ', ' __delitem__ ', ' __dir__ ', ' __ Doc__ ', ' __eq__ ', ' __format__ ', ' __ge__ ', ' __getattribute__ ', ' __getitem__ ', ' __gt__ ', ' __hash__ ', ' __init__ ', ' __init_ Subclass__ ', ' __iter__ ', ' __le__ ', ' __len__ ', ' __lt__ ', ' __ne__ ', ' __new__ ', ' __reduce__ ', ' __reduce_ex__ ', ' __repr__ ', ' __setattr__ ', ' __setitem__ ', ' __sizeof__ ', ' __str__ ', ' __subclasshook__ ', ' clear ', ' copy ', ' Fromkeys ', ' get ', ' items ', ' Keys ', ' Pop ', ' Popitem ', ' setd ' Efault ', ' Update ', ' values '] #fromkeys #用给定的键建立新的字典, each key defaults to none (mass production of new dictionaries) >>> Di.fromkeys ({' A ', ' B ', ' C '}) {' B ': None, ' C ': None, ' A ': none} #用给定的键建立新的字典, each key is Custom 123 >>> Di.fromkeys ({' A ', ' B ', ' C '},123) {' B ': 123, ' C ': 12 3, ' a ': 123}>>> Help (Di.fromkeys) Help on built-in function Fromkeys:fromkeys (iterable, Value=none,/) method of B Uiltins.type instance Returns a new dict with keys from iterable and values equal to value. #字典取值; value exists, then return value, no default return None, Also         Customizable >>> di {' W ': 123, ' E ': 456, ' R ': 789} >>> Di.get (' W ') 123 >>> di.get (' Q ') >>> di {' W ': 123, ' E ': 456, ' R ': 789} >>> di.get (' Q ', ' I don't exist ') ' I don't exist ' #items, display the dictionary as a tuple in the list Each >>> di.items (Dict_items (' W ', 123), (' E ', 456), (' R ', 789)]) >>> list (Di.items ()) #查 Look at every item in the dictionary [(' W ', 123),(' e ', 456), (' R ', 789)] #以列表的形式查看字典的所有键 >>> Di.keys () Dict_keys ([' W ', ' e ', ' R ']) #以列表的形式查看字典的所有值 >>& Gt Di.values () dict_values ([123, 456, 789]) #pop, specify the key and delete the corresponding value. If the key does not exist, you can customize the return value >>> Help (di.pop) to built-in function Pop:pop (...) method of Builtins.dict Instanc        E D.pop (K[,d])-V, remove specified key and return the corresponding value. If key is not found, D is returned if given, otherwise keyerror is raised >>> di {' W ': 123, ' E ': 456, ' R ':    789} >>> Di.pop (' e ') 456 >>> di {' W ': 123, ' R ': 789} >>> Di.pop (' W ', ' R ') 123     >>> di {' R ': 789} >>> di.pop (' Q ', ' I don't exist ') ' I don't exist ' #popitem, random Delete dictionary (no object required) >>> di {' R ': 789, ' W ': 123} >>> di {' R ': 789, ' W ': 123} >>> Di.popitem () (' W ', 123) >> > di {' R ': 789} #类似get, there is a return value, the update to the dictionary does not exist, the corresponding value defaults to none, can also be customized >>> di.setdefault (' R ') 789;>> Di.setdefault (' W ', 123) 123 >>> di {' R ': 789, ' W ': 123} >>> di.setdefault (' Q ') & gt;>> di {' R ': 789, ' W ': 123, ' Q ': none# Add and update a dictionary content to the original dictionary >>> di {' R ': 789, ' W ': 123, ' Q ': None } >>> di1={' P ': 234, ' Q ': 123} >>> di.update (di1) >>> di {' P ': 234, ' R ': 789, ' W ': 123    , ' Q ': 123} >>> di={' x ': [123,456]} >>> di {' x ': [123, 456]} >>> di[' W ']=123 >>> di {' x ': [123, 456], ' W ': 123}

3. Operators

算数运算符： +，-，*，/，%，**，//    赋值运算符： = += -= *= /= %= **=    比较运算符： ==  !=  >  <  >=  <=    成员运算符： in , not in    身份运算符： is  , is not        判断两个名字是否指向同一个对象，当id相同时返回True（==比较运算时判断的值）    逻辑运算符： and  or  not        and(与)  两个条件都满足是才返回True        or(或)   有一个条件满足了就返回True        not(非)  取反    计算顺序：默认，运算符优先级表决定了那个运算符在别的运算符之前计算。然而，如果你想改变它们的顺序，你得使用圆括号    结合规律：运算符通常由左向右结合，及具有相同优先级的运算符按照从左向右的顺序计算    **                          #幂运算    = - * / %                   #算数运算符    < > <= >=                   #比较运算符    ==  !=                      #比较运算符    = %= /= -= += *= **=        #赋值运算符    is  is not                  #身份运算符    in  not in                  #成员运算符    not  >  and  > or           #逻辑运算符>>> a=1;b=2>>> a==bFalse>>> a!=bTrue>>> a is bFalse>>> a is not bTrue>>> a==1 and b==3False>>> a==1 or b==3True>>> not b==3True>>> a==1 and not b==3True

Python basic data type (iv)-collections and operators-python3 notes