python range() function like postgresql generate_series()

最新推荐文章于 2025-09-11 21:03:21 发布

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原文链接：https://yq.aliyun.com/articles/14558

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#python #数据库

本文详细介绍了Python中的range()函数用法，包括如何生成数字序列、指定起始值和步长，以及如何结合len()函数遍历序列。此外还对比了range()与列表的区别，并介绍了迭代器的概念。

>>> range(0,10)

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

>>> len(range(0,10))

>>> range(9,20,3)

[9, 12, 15, 18]

同时因为range()返回的是一个list, 所以可以用在for循环中.

>>> words = ['cat', 'window', 'defenestrate']

>>> for i in range(len(words)):

... print(i, words[i])

...

(0, 'cat')

(1, 'window')

(2, 'defenestrate')

digoal=# select generate_series(1,10);

generate_series

-----------------

(10 rows)

[参考]

1. https://docs.python.org/3/tutorial/controlflow.html

4.3. The range() Function?

If you do need to iterate over a sequence of numbers, the built-in function range() comes in handy. It generates arithmetic progressions:

>>>

>>> for i in range(5):
...     print(i)
...
0
1
2
3
4

The given end point is never part of the generated sequence; range(10) generates 10 values, the legal indices for items of a sequence of length 10. It is possible to let the range start at another number, or to specify a different increment (even negative; sometimes this is called the ‘step’):

range(5, 10)
   5 through 9

range(0, 10, 3)
   0, 3, 6, 9

range(-10, -100, -30)
  -10, -40, -70

To iterate over the indices of a sequence, you can combine range() and len() as follows:

>>>

>>> a = ['Mary', 'had', 'a', 'little', 'lamb']
>>> for i in range(len(a)):
...     print(i, a[i])
...
0 Mary
1 had
2 a
3 little
4 lamb

In most such cases, however, it is convenient to use the enumerate() function, see Looping Techniques.

A strange thing happens if you just print a range:

>>>

>>> print(range(10))
range(0, 10)

In many ways the object returned by range() behaves as if it is a list, but in fact it isn’t. It is an object which returns the successive items of the desired sequence when you iterate over it, but it doesn’t really make the list, thus saving space.

We say such an object is iterable, that is, suitable as a target for functions and constructs that expect something from which they can obtain successive items until the supply is exhausted. We have seen that the for statement is such an iterator. The function list() is another; it creates lists from iterables:

>>>