在python 3中将字符串转换为数字列表

Question

This tells us the way to prepare a list of numbers, including a range of continues numbers or discontinues numbers.

For example, list(range(1,10)) + [20,30,40] + list(range(400,410)) will return [1, 2, 3, 4, 5, 6, 7, 8, 9, 20, 30, 40, 400, 401, 402, 403, 404, 405, 406, 407, 408, 409] .

But can I make it simpler by only inputting a string like "1-10, 20, 30, 40, 400-410" ?

I can write a function using a for-loop to go through the numbers. Is there a more efficient way to write the function without using a for-loop?

Answer 1

You can use a nested list comprehension, checking whether the current part contains a - and using either a range or creating a one-elemented list accordingly:

>>> s = "1-10, 20, 30, 40, 400-410"
>>> [n for part in s.split(", ") for n in (range(*map(int, part.split("-"))) if "-" in part else [int(part)])]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 20, 30, 40, 400, 401, 402, 403, 404, 405, 406, 407, 408, 409]

Maybe split this up, for readability:

>>> to_list = lambda part: range(*map(int, part.split("-"))) if "-" in part else [int(part)]
>>> [n for part in s.split(", ") for n in to_list(part)]

Note: As in your first example, this will translate "1-10" to [1, 2, ..., 9] , without 10 .

---

As noted in comments, this will not work for negative numbers, though, trying to split -3 or -4--2 into pairs of numbers. For this, you could use regular expressions...

>>> def to_list(part):
...     m =re.findall(r"(-?\d+)-(-?\d+)", part)
...     return range(*map(int, m[0])) if m else [int(part)]
...
>>> s = "-10--5, -4, -2-3"
>>> [n for part in s.split(", ") for n in to_list(part)]
[-10, -9, -8, -7, -6, -4, -2, -1, 0, 1, 2]

... or just use a different delimiter for ranges, eg -10:-5 .

Answer 2

I suggest that you instead write a function that allows to create more complex, piecewise ranges.

def piecewise_range(*args):
    for arg in args:
        yield from range(*arg)

piecewise_range((1, 10), (20, 50, 10), (400, 410))

The function piecewise_range then outputs a generator, so it allows you to have more complex range patterns and to preserve range laziness.

Answer 3

Depending on where your input strings come from, you might do with something like this, named whatever you would want to name it:

import re

def gen_nums(input_string):
    out = []
    for item in re.split(r',\s*', input_string):
        if '-' in item:
            start, end = item.split('-')
            out.extend(range(int(start), int(end)))
        else:
            out.append(int(item))
    return out