Generator-expression, getting the same results of using append or extend in a for-loop

Question

usingAppend = []; usingExtend = []; usingLC = []

d = {'pKey_b': 'vb1', 'pKey_e': 've1', 'pKey_c': 'vc1', 'pKey_a': 'va1', 'pKey_d': 'vd1'}

Using append in the for-loop gives a list with sublists

for k, v in sorted(d.iteritems()):
    usingAppend.append([k, v])
print '\n', usingAppend

'''
[
 ['pKey_a', 'va1'],
 ['pKey_b', 'vb1'],
 ['pKey_c', 'vc1'],
 ['pKey_d', 'vd1'],
 ['pKey_e', 've1']
]
'''

Using extend in the for-loop gives a single list

for k, v in sorted(d.iteritems()):
    usingExtend.extend((k, v))
print '\n', usingExtend

'''
['pKey_a', 'va1', 'pKey_b', 'vb1', 'pKey_c', 'vc1', 'pKey_d', 'vd1', 'pKey_e', 've1']
'''

Using this generator expression gives the same results as using append in a for loop, a list with sublists

usingLC = sorted([k, v] for k, v in d.iteritems())
print '\n', usingLC

'''
[
 ['pKey_a', 'va1'],
 ['pKey_b', 'vb1'],
 ['pKey_c', 'vc1'],
 ['pKey_d', 'vd1'],
 ['pKey_e', 've1']
]
'''

My question is, is there a way to set up the generator expression to give the same results as using extend in a for-loop

Answer 1

You use double looping:

[i for k, v in sorted(d.iteritems()) for i in (k, v)]

or

[i for item in sorted(d.iteritems()) for i in item]

or itertools.chain.from_iterable():

from itertools import chain

list(chain.from_iterable(item for item in sorted(d.iteritems())))

although you could just use:

list(chain.from_iterable(sorted(d.iteritems())))

in these cases.

Demo:

>>> d = {'pKey_b': 'vb1', 'pKey_e': 've1', 'pKey_c': 'vc1', 'pKey_a': 'va1', 'pKey_d': 'vd1'}
>>> [i for k, v in sorted(d.iteritems()) for i in (k, v)]
['pKey_a', 'va1', 'pKey_b', 'vb1', 'pKey_c', 'vc1', 'pKey_d', 'vd1', 'pKey_e', 've1']
>>> from itertools import chain
>>> list(chain.from_iterable(item for item in sorted(d.iteritems())))
['pKey_a', 'va1', 'pKey_b', 'vb1', 'pKey_c', 'vc1', 'pKey_d', 'vd1', 'pKey_e', 've1']
>>> list(chain.from_iterable(sorted(d.iteritems())))
['pKey_a', 'va1', 'pKey_b', 'vb1', 'pKey_c', 'vc1', 'pKey_d', 'vd1', 'pKey_e', 've1']