I've got a list of strings, where each string contains a datestring in the second part, e.g.:
alist = ['foo_20150901', 'bar_20150801', 'baz_20150701']
Now I want to have them ordered ascending with respect to the date. I thought this would work like this:
slist = alist.sort(key =(lambda k: int(k.split('_')[-1])))
However, printing slist yields None. What's wrong here?
Look up the documentation for sort, it explicitly states *IN PLACE* and returning None:
Docstring: L.sort(key=None, reverse=False) -> None -- stable sort *IN PLACE*
Type: method_descriptor
To return the sorted list you need to use sorted instead:
In [5]: sorted??
Docstring:
Return a new list containing all items from the iterable in ascending order.
A custom key function can be supplied to customise the sort order, and the
reverse flag can be set to request the result in descending order.
Type: builtin_function_or_method
L.sort() sorts the list in-place returning None, you want the sorted function:
sorted(iterable, key=None, reverse=False)
Return a new list containing all items from the iterable in ascending order.
slist = sorted(alist, key=lambda k: int(k.split('_')[-1]))
alist = ['foo_20150901', 'bar_20150801', 'baz_20150701']
alist.sort(key =(lambda k: int(k.split('_')[-1])))
print alist
Output:
['baz_20150701', 'bar_20150801', 'foo_20150901']
