总结分析列表、元组、字典、集合的相同与区别之处,只有彻底分清之后,就会在应用的时候,得心应手。
len()
要确定列表中有多少项,请使用len()函数
thislist = ["apple", "banana", "cherry"]
print(len(thislist))
要确定一个元组有多少项,请使用len()函数
thistuple = ("apple", "banana", "cherry")
print(len(thistuple))
要确定一个集合有多少项,请使用len()函数。
thisset = {"apple", "banana", "cherry"}
print(len(thisset))
要确定字典有多少项,请使用len()函数
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964,
"year": 2020
}
print(len(thisdict))
列表项已编制索引,您可以通过引用索引号来访问它们
thislist = ["apple", "banana", "cherry"]
print(thislist[1])
您可以通过引用方括号内的索引号来访问元组项
thistuple = ("apple", "banana", "cherry")
print(thistuple[1])
in
关键字要确定列表中是否存在指定项,请使用in
关键字
thislist = ["apple", "banana", "cherry"]
if "apple" in thislist:
print("Yes, 'apple' is in the fruits list")
要确定元组中是否存在指定项,请使用in
关键字
thistuple = ("apple", "banana", "cherry")
if "apple" in thistuple:
print("Yes, 'apple' is in the fruits tuple")
检查集合中是否有“香蕉”
thisset = {"apple", "banana", "cherry"}
print("banana" in thisset)
要确定字典中是否存在指定的键,请使用in关键字
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
if "model" in thisdict:
print("Yes, 'model' is one of the keys in the thisdict dictionary")
可以使用for循环遍历列表项
thislist = ["apple", "banana", "cherry"]
for x in thislist:
print(x)
可以使用for循环遍历元组项
thistuple = ("apple", "banana", "cherry")
for x in thistuple:
print(x)
在集合中循环,并打印值
thisset = {"apple", "banana", "cherry"}
for x in thisset:
print(x)
循环字典
for x in thisdict:
print(thisdict[x])
还可以使用values()方法返回字典的值
for x in thisdict.values():
print(x)
可以使用keys()方法返回字典的键
for x in thisdict.keys():
print(x)
使用items()方法循环遍历键和值
for x, y in thisdict.items():
print(x, y)
clear()方法清空列表。
thislist = ["apple", "banana", "cherry"]
thislist.clear()
print(thislist)
clear()方法清空集合
thisset = {"apple", "banana", "cherry"}
thisset.clear()
print(thisset)
clear()方法清空字典
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict.clear()
print(thisdict)
del关键字还会删除指定的索引
thislist = ["apple", "banana", "cherry"]
del thislist[0]
print(thislist)
del关键字也可以完全删除列表。
thislist = ["apple", "banana", "cherry"]
del thislist
del关键字将完全删除集合
thisset = {"apple", "banana", "cherry"}
del thisset
print(thisset)
del关键字删除字典具有指定键名的项
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
del thisdict["model"]
print(thisdict)
remove()方法删除指定的项。
thislist = ["apple", "banana", "cherry"]
thislist.remove("banana")
print(thislist)
要删除集合中的项,请使用remove()或discard()方法。
thisset = {"apple", "banana", "cherry"}
thisset.remove("banana")
print(thisset)
pop()方法删除列表指定的索引。
thislist = ["apple", "banana", "cherry"]
thislist.pop(1)
print(thislist)
您也可以使用pop()方法删除一个项目,但此方法将删除最后一个项目。请记住,集合是无序的,因此您将不知道删除了哪些项
。
thisset = {"apple", "banana", "cherry"}
x = thisset.pop()
print(x)
print(thisset)
pop()方法移除字典具有指定键名的项
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict.pop("model")
print(thisdict)
insert()方法在指定的索引处插入项
thislist = ["apple", "banana", "cherry"]
thislist.insert(2, "watermelon")
print(thislist)
要将项目添加到列表的末尾,请使用append()方法
thislist = ["apple", "banana", "cherry"]
thislist.append("orange")
print(thislist)
要将其他列表中的元素附加到当前列表,请使用extend()方法。
thislist = ["apple", "banana", "cherry"]
tropical = ["mango", "pineapple", "papaya"]
thislist.extend(tropical)
print(thislist)
extend()方法不必附加列表,您可以添加任何可迭代对象(元组、集合、字典等)。
thislist = ["apple", "banana", "cherry"]
thistuple = ("kiwi", "orange")
thislist.extend(thistuple)
print(thislist)
如果不指定索引,则pop()方法将删除最后一项。
thislist = ["apple", "banana", "cherry"]
thislist.pop()
print(thislist)
列表理解提供了循环列表的最短语法:newlist = [*expression* for *item* in *iterable* if *condition* == True]
thislist = ["apple", "banana", "cherry"]
[print(x) for x in thislist]
fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = [x for x in fruits if "a" in x]
print(newlist)
newlist = [x.upper() for x in fruits]
列表对象有一个sort()方法,默认情况下,该方法将按字母数字升序对列表进行排序
thislist = ["orange", "mango", "kiwi", "pineapple", "banana"]
thislist.sort()
print(thislist)
在排序列表时,我们可以使用内置函数作为关键函数
thislist = ["banana", "Orange", "Kiwi", "cherry"]
thislist.sort(key = str.lower)
print(thislist)
reverse()方法反转元素的当前排序顺序。
thislist = ["banana", "Orange", "Kiwi", "cherry"]
thislist.reverse()
print(thislist)
有多种方法可以复制,一种方法是使用内置的列表方法copy()。
您不能简单地通过键入list2=list1复制列表,因为:list2仅仅是对list1的引用,并且在list1中所做的更改也将自动在list2中进行。
thislist = ["apple", "banana", "cherry"]
mylist = thislist.copy()
print(mylist)
制作副本的另一种方法是使用内置方法list()。
thislist = ["apple", "banana", "cherry"]
mylist = list(thislist)
print(mylist)
在Python中,有几种方法可以连接或串联两个或多个列表。最简单的方法之一是使用+运算符。
list1 = ["a", "b", "c"]
list2 = [1, 2, 3]
list3 = list1 + list2
print(list3)
也可以使用extend()方法,其目的是将元素从一个列表添加到另一个列表
list1 = ["a", "b" , "c"]
list2 = [1, 2, 3]
list1.extend(list2)
print(list1)
要创建只有一个项的元组,必须在该项后添加逗号,否则Python将无法将其识别为元组。
thistuple = ("apple",)
print(type(thistuple))
#NOT a tuple
thistuple = ("apple")
print(type(thistuple))
您可以将元组转换为列表,更改列表,然后将列表转换回元组。
x = ("apple", "banana", "cherry")
y = list(x)
y[1] = "kiwi"
x = tuple(y)
print(x)
将元组添加到元组。您可以将元组添加到元组中,因此如果要添加一个(或多个)项,请使用该项创建一个新元组,并将其添加到现有元组中.
thistuple = ("apple", "banana", "cherry")
y = ("orange",)
thistuple += y
print(thistuple)
我们可以将值提取回变量中,这称为“拆包”
fruits = ("apple", "banana", "cherry")
(green, yellow, red) = fruits
print(green)
print(yellow)
print(red)
如果变量的数量小于值的数量,则可以在变量名中添加*号,这些值将作为列表分配给变量
fruits = ("apple", "banana", "cherry", "strawberry", "raspberry")
(green, yellow, *red) = fruits
print(green)
print(yellow)
print(red)
要连接两个或多个元组,可以使用+运算符
tuple1 = ("a", "b" , "c")
tuple2 = (1, 2, 3)
tuple3 = tuple1 + tuple2
print(tuple3)
如果要将元组的内容乘以给定的次数,可以使用*运算符
fruits = ("apple", "banana", "cherry")
mytuple = fruits * 2
print(mytuple)
创建集后,不能更改其项,但可以添加新项。
thisset = {"apple", "banana", "cherry"}
thisset.add("orange")
print(thisset)
要将其他集合中的项添加到当前集合中,请使用update()方法。
thisset = {"apple", "banana", "cherry"}
tropical = {"pineapple", "mango", "papaya"}
thisset.update(tropical)
print(thisset)
可以使用union()方法返回包含两个集合中所有项的新集合,也可以使用update()方法将一个集合中的所有项插入另一个集合
set1 = {"a", "b" , "c"}
set2 = {1, 2, 3}
set3 = set1.union(set2)
print(set3)
set1 = {"a", "b" , "c"}
set2 = {1, 2, 3}
set1.update(set2)
print(set1)
intersection_update()方法将只保留两个集合中存在的项。
x = {"apple", "banana", "cherry"}
y = {"google", "microsoft", "apple"}
x.intersection_update(y)
print(x)
intersection()方法将返回一个新的集合,该集合只包含两个集合中存在的项。
x = {"apple", "banana", "cherry"}
y = {"google", "microsoft", "apple"}
z = x.intersection(y)
print(z)
symmetric_difference_update()方法将只保留两个集合中不存在的元素。
x = {"apple", "banana", "cherry"}
y = {"google", "microsoft", "apple"}
x.symmetric_difference_update(y)
print(x)
symmetric_difference()方法将返回一个新的集合,该集合只包含两个集合中不存在的元素。
x = {"apple", "banana", "cherry"}
y = {"google", "microsoft", "apple"}
z = x.symmetric_difference(y)
print(z)
您可以通过在方括号内引用字典的键名来访问字典的项
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
x = thisdict["model"]
还有一个名为get()的方法,它将给出相同的结果
x = thisdict.get("model")
keys()方法将返回字典中所有键的列表。
x = thisdict.keys()
values()方法将返回字典中所有值的列表。
x = thisdict.values()
items()方法将返回字典中的每个项,作为列表中的元组。
x = thisdict.items()
返回的列表是字典项的视图,这意味着对字典所做的任何更改都将反映在项列表中。
car = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
x = car.items()
print(x) #before the change
car["year"] = 2020
print(x) #after the change
popitem()方法删除最后插入的项(在3.7之前的版本中,将删除随机项)
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict.popitem()
print(thisdict)
您不能简单地通过键入dict2=dict1来复制字典,因为:dict2将仅是对dict1的引用,在dict1中所做的更改也将自动在dict2中进行。
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
mydict = thisdict.copy()
print(mydict)
字典可以包含字典,这称为嵌套字典。
myfamily = {
"child1" : {
"name" : "Emil",
"year" : 2004
},
"child2" : {
"name" : "Tobias",
"year" : 2007
},
"child3" : {
"name" : "Linus",
"year" : 2011
}
}
child1 = {
"name" : "Emil",
"year" : 2004
}
child2 = {
"name" : "Tobias",
"year" : 2007
}
child3 = {
"name" : "Linus",
"year" : 2011
}
myfamily = {
"child1" : child1,
"child2" : child2,
"child3" : child3
}
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