python：检查任意数量的嵌套列表以得出是否为空的结论

Question

so basically I'm trying to create a function that will check a list which may or may not contain many nested layers of lists, to see if they are all empty.

so

empty([]) will return true so will empty([['']]) and so will empty([[[]]])

I've tried

def empty(seq):
     try:
         return all(map(empty, seq))
     except TypeError:
         return False

but running into RuntimeError: maximum recursion depth exceeded error when I run this.

The problematic case string is this : ["[u'3D Blu-ray Disc\\\™ Player (BD-D7500)']"] I have no idea why that is causing this problem

["[u'3D Blu-ray Disc\\u2122 Player (BD-D7500)']"]
maximum recursion depth exceeded in cmp
Traceback (most recent call last):
  File "./dashboard.py", line 583, in download
    return get_rows_from_db(str(job.id), job.url,taskid, options,trial)
  File "./dashboard.py", line 123, in get_rows_from_db
    print "B " + empty(col)
  File "./dashboard.py", line 52, in empty
    for item in seq)
  File "./dashboard.py", line 52, in <genexpr>
    for item in seq)
  File "./dashboard.py", line 52, in empty
    for item in seq)
  File "./dashboard.py", line 52, in <genexpr>
    for item in seq)
  File "./dashboard.py", line 52, in empty
    for item in seq)
  File "./dashboard.py", line 52, in <genexpr>
    for item in seq)
  File "./dashboard.py", line 52, in empty
    for item in seq)
  File "./dashboard.py", line 52, in <genexpr>
    for item in seq)
  File "./dashboard.py", line 52, in empty
    for item in seq)
  File "./dashboard.py", line 52, in <genexpr>
    for item in seq)
  File "./dashboard.py", line 52, in empty
    for item in seq)
  File "./dashboard.py", line 52, in <genexpr>
    for item in seq)
  File "./dashboard.py", line 52, in empty
    for item in seq)
  File "./dashboard.py", line 52, in <genexpr>
    for item in seq)
  File "./dashboard.py", line 52, in empty
    for item in seq)
  File "./dashboard.py", line 52, in <genexpr>
    for item in seq)
  File "./dashboard.py", line 52, in empty
    for item in seq)
  File "./dashboard.py", line 52, in <genexpr>
    for item in seq)
  File "./dashboard.py", line 52, in empty
    for item in seq)
  File "./dashboard.py", line 52, in <genexpr>
    for item in seq)
  File "/usr/lib/python2.7/abc.py", line 132, in __instancecheck__
    if subclass is not None and subclass in cls._abc_cache:
  File "/usr/lib/python2.7/_weakrefset.py", line 73, in __contains__
    return wr in self.data
RuntimeError: maximum recursion depth exceeded in cmp

Answer 1

def empty(L_or_I):
    if not L_or_I:
       return True
    if isinstance(L_or_I,(list,tuple)):
       return all(empty(x) for x in L_or_I)
    return False

I guess ... maybe

Answer 2

If a list of 0 is an "empty", Joran answer is certainly correct.

If you only want to check iterable, I would suggest:

import collections
def empty(e):
    if not isinstance(e, collections.Iterable):
        return False
    if not e:
        return True
    return all(empty(x) for x in e)

Answer 3

This function satisfies each of the test cases you provide.

import collections


def empty(seq):
    if isinstance(seq, basestring):
        return seq == ''
    return all(empty(item)
               if isinstance(item, collections.Sequence)
               else False
               for item in seq)

assert empty([])
assert empty([['']])
assert empty([[[]]])
assert not empty([[[], 1]])
assert empty(u'')
assert not empty(u'1')
assert not empty(["[[u'3D Blu-ray Disc\\u2122 Player (BD-D7500)']"])