Question

有没有办法可以优雅地将函数输入转换为列表？在确保输入已经是列表时，它会保留在顶级列表中吗？

例如：

def pprint(input):
    for i in input:
        print(i)

a = ['Hey!']
pprint(a) # >>>>'Hey!'

b = 'Hey!'
pprint(b) # >>>> 'H', 'e', 'y', '!'  # NOT WANTED BEHAVIOR

我目前的方法是做一个类型检查，这不是非常pythonic也不优雅。有更好的解决方案吗？

# possible solution 1
def pprint2(input):
    if type(input) not in [list, tuple]:
        input = [input]
    for i in input:
        print(i)

# possible solution 2
      # but I would really really like to keep the argument named! (because I have other named arguments in my actual function), but it does have the correct functionality!
def pprint3(*args):
    for i in input:
        print(i)

Answer 1

使用isinstance和collections.Iterable：

from collections import Iterable
def my_print(inp):
    #As suggested by @user2357112
    if not isinstance(inp, Iterable) or isinstance(inp, basestring):
        inp = [inp]                           #use just `str` in py3.x
    for item in inp:  #use `yield from inp` in py3.x                     
        yield item
...         
>>> for x in my_print('foo'):
...     print x
...     
foo
>>> for x in my_print(range(3)):
    print x
...     
0
1
2
>>> for x in my_print(dict.fromkeys('abcd')):
    print x
...     
a
c
b
d

_{请注意pprint是python中标准模块的名称，所以我建议你使用不同的变量名。}

Answer 2

利用assert和isinstance

>>> inp = "String to test"
>>> try:
...     assert not isinstance(inp, basestring)
...     for i in inp:
...        print i
... except AssertionError:
...     print inp
... 
String to test

Python强制输入为列表

2 个答案: