元组/列表之间的区别是什么?它们的优点/缺点是什么?
当前回答
List是可变的,tuples是不可变的。可变和不可变之间的主要区别是当您试图追加一个项时内存的使用。
当你创建一个变量时,一些固定的内存被分配给变量。如果它是一个列表,则分配的内存比实际使用的要多。例如,如果当前内存分配是100个字节,当你想追加第101个字节时,可能会再分配100个字节(在这种情况下总共是200个字节)。
然而,如果你知道你不经常添加新元素,那么你应该使用元组。Tuples精确地分配所需的内存大小,从而节省内存,特别是当您使用大块内存时。
其他回答
从5.3的文档中引证的方向。元组和序列:
虽然元组可能看起来类似于列表,但它们通常用于不同的情况和不同的目的。元组是不可变的,通常包含不同的元素序列,可以通过解包(参见本节后面的内容)或索引(对于namedtuples,甚至可以通过属性访问)访问这些元素。列表是可变的,它们的元素通常是同构的,并通过遍历列表来访问。
列表是可变的;元组不是。
从docs.python.org/2/tutorial/datastructures.html
元组是不可变的,通常包含的异构序列 通过解包访问的元素(参见本节后面的内容) 或者索引(在命名元组的情况下甚至通过属性)。列表 是可变的,它们的元素通常是同质的和 通过遍历列表来访问。
list和tuple的区别
元组和列表在Python中看起来都是相似的序列类型。
Literal syntax We use parenthesis () to construct tuples and square brackets [ ] to get a new list. Also, we can use call of the appropriate type to get required structure — tuple or list. someTuple = (4,6) someList = [2,6] Mutability Tuples are immutable, while lists are mutable. This point is the base the for the following ones. Memory usage Due to mutability, you need more memory for lists and less memory for tuples. Extending You can add a new element to both tuples and lists with the only difference that the id of the tuple will be changed (i.e., we’ll have a new object). Hashing Tuples are hashable and lists are not. It means that you can use a tuple as a key in a dictionary. The list can't be used as a key in a dictionary, whereas a tuple can be used tup = (1,2) list_ = [1,2] c = {tup : 1} # ok c = {list_ : 1} # error Semantics This point is more about best practice. You should use tuples as heterogeneous data structures, while lists are homogenous sequences.
列表是可变的,元组是不可变的。 考虑一下这个例子。
a = ["1", "2", "ra", "sa"] #list
b = ("1", "2", "ra", "sa") #tuple
现在改变list和tuple的索引值。
a[2] = 1000
print a #output : ['1', '2', 1000, 'sa']
b[2] = 1000
print b #output : TypeError: 'tuple' object does not support item assignment.
因此证明下面的代码是无效的元组,因为我们试图更新一个元组,这是不允许的。
list和tuple的区别
Literal someTuple = (1,2) someList = [1,2] Size a = tuple(range(1000)) b = list(range(1000)) a.__sizeof__() # 8024 b.__sizeof__() # 9088 Due to the smaller size of a tuple operation, it becomes a bit faster, but not that much to mention about until you have a huge number of elements. Permitted operations b = [1,2] b[0] = 3 # [3, 2] a = (1,2) a[0] = 3 # Error That also means that you can't delete an element or sort a tuple. However, you could add a new element to both list and tuple with the only difference that since the tuple is immutable, you are not really adding an element but you are creating a new tuple, so the id of will change a = (1,2) b = [1,2] id(a) # 140230916716520 id(b) # 748527696 a += (3,) # (1, 2, 3) b += [3] # [1, 2, 3] id(a) # 140230916878160 id(b) # 748527696 Usage As a list is mutable, it can't be used as a key in a dictionary, whereas a tuple can be used. a = (1,2) b = [1,2] c = {a: 1} # OK c = {b: 1} # Error
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