从可变长度字符串中解析值的最佳方法是什么？

Question

Suppose I have a string of integers separated by commas of variable length. What is the best way to split the string and update variables with values if they exist?

Currently, I have the following.

a, b, c = 10, 10, 1    #default values
mylist = [int(x) for x in input.split(',')]
if len(mylist) == 2: a, b = mylist
else: a, b, c = mylist

Is there a more efficient way of doing this?

Answer 1

a, b, c = 10, 10, 1    #default values
mylist = [int(x) for x in input.split(',')]
a, b, c = mylist + [a, b, c][len(mylist):]

I think the reason this is ugly is that it's non-Pythonic to treat local variables in aggregate; instance members would be more appropriate.

Answer 2

You could use a helper function:

def f(a=10, b=10, c=1):
    return a, b, c

a, b, c = f(*map(int, input.split()))

This won't be faster – it's just a different way to do it that just crossed my mind.

Answer 3

defaults=[10,10,1]
mylist=[int(x) for x in ipt.split(',')]
defaults[:len(mylist)]=mylist
a,b,c=defaults

This changes defaults though... You to avoid that, something like this would work:

defaults=[10,10,1]
mylist=[int(x) for x in ipt.split(',')]
temp_defaults=defaults[:]
temp_defaults[:len(mylist)]=mylist
a,b,c=temp_defaults

Also, be careful using input as a variable name. It's the name of a python built-in so you're removing your easy access to that function.

Answer 4

Use slicing to combine the user input with the list of default arguments:

>>> defaults = [10, 10, 1]
>>> user_input = '15 20'
>>> user_ints = map(int, user_input.split())
>>> combined = user_ints + defaults[len(user_ints):]
>>> a, b, c = combined

Answer 5

izip_longest allows to take the length of the default values if longer:

>>> from itertools import izip_longest
>>> inp = '3, 56'
>>> a, b, c = [i if i else j for i, j in izip_longest([int(x) for x in inp.split(',')], (10, 10, 1))]
>>> a, b, c
(3, 56, 1)

Answer 6

a, b, c = (map(int, user_input.split(',')) + [20,20,10])[:3]

or

def parse(user_input, *args):
    return (map(int, user_input.split(',')) + list(args))[:len(args)]

>>> a, b, c = parse('1,2', 20, 20, 10)
>>> a, b, c
(1, 2, 20)
>>> a, b, c, d = parse('1,2,3,4,5', 0, 0, 0, 0)
>>> a, b, c, d
(1, 2, 3, 4)