問題描述

我了解如何在 for 循環中使用 range() 和 zip() 等函數.但是我希望 range() 輸出一個列表 - 很像 unix shell 中的 seq .如果我運行以下代碼:

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)

輸出是range(10)，表明它不是一個列表，而是一種不同類型的對象.zip() 在打印時有類似的行為，輸出類似

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">

所以我的問題是它們是什么，制作它們有什么優勢，以及如何在不循環它們的情況下將它們的輸出輸出到列表?

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?

推薦答案

你必須使用 Python 3.

You must be using Python 3.

在 Python 2 中，對象 zip 和 range 確實按照您的建議行事，返回列表.它們已更改為類似 generator 的對象，這些對象按需生成元素，而不是將整個列表擴展為記憶.一個優勢是在它們的典型用例中效率更高(例如迭代它們).

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).

惰性"版本也存在于 Python 2.x 中，但它們有不同的名稱，即 xrange 和 itertools.izip.

The "lazy" versions also exist in Python 2.x, but they have different names i.e. xrange and itertools.izip.

要一次將所有輸出檢索到熟悉的列表對象中，您可以簡單地調用 list 來迭代并使用內容:

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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