Python range()和zip()对象类型 [英] Python range() and zip() object type
问题描述
我理解如何在for循环中使用 range()
和 zip()
等函数。但是我希望 range()
输出一个列表 - 就像unix shell中的 seq
一样。如果我运行以下代码:
I understand how functions like range()
and zip()
can be used in a for loop. However I expected range()
to output a list - much like seq
in the unix shell. If I run the following code:
a=range(10)
print(a)
输出 range(10)
,表明它不是列表但是一种不同类型的物体。 zip()
在打印时有类似的行为,输出类似
The output is range(10)
, suggesting it's not a list but a different type of object. zip()
has a similar behaviour when printed, outputting something like
<zip object at "hexadecimal number">
所以我的问题是他们是什么,有什么优势让他们这样做,我怎么能得到他们的输出到列表而不循环它们?
So my question is what are they, what advantages are there to making them this, and how can I get their output to lists without looping over them?
推荐答案
你必须使用Python 3.
You must be using Python 3.
在Python 2中,对象 zip
和范围
确实按照您的建议行事,返回名单。它们被更改为生成器类似的对象,这些对象按需生成元素,而不是将整个列表扩展为记忆。一个优点是它们在典型用例中的效率更高(例如迭代它们)。
In Python 2, the objects zip
and range
did behave as you were suggesting, returning lists. They were changed to generator-like objects which produce the elements on demand rather than expand an entire list into memory. One advantage was greater efficiency in their typical use-cases (e.g. iterating over them).
Python 2.x中也存在懒惰版本,但它们有所不同名称是 xrange
和 itertools.izip
。
The "lazy" versions also exist in Python 2.x, but they have different names i.e. xrange
and itertools.izip
.
To将所有输出一次检索到熟悉的列表对象中,您可以简单地调用 list
来迭代并使用内容:
To retrieve all the output at once into a familiar list object, you may simply call list
to iterate and consume the contents:
>>> list(range(3))
[0, 1, 2]
>>> list(zip(range(3), 'abc'))
[(0, 'a'), (1, 'b'), (2, 'c')]
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