>>> i = 0
>>> seq = ['one', 'two', 'three']
>>> for element in seq:
… seq[i] = ‘%d: %s’ % (i, seq[i])
… i += 1
…
>>> seq
['0: one', '1: two', '2: three']
>>> seq = ['one', 'two', 'three']
>>> for i, element in enumerate(seq):
… seq[i] = ‘%d: %s’ % (i, seq[i])
…
>>> seq
['0: one', '1: two', '2: three']
>>> def _treatment(pos, element):
… return ‘%d: %s’ %(pos, element)
…
>>> seq = ['one', 'two', 'three']
>>> [_treatment(i, e1) for i, e1 in enumerate(seq)]
['0: one', '1: two', '2: three']