Question

Essentially I have a list of items each with a different type such as

['a',1,'b',2,3,'c'] 

or

[{"A":1},1,{"B":2},{"C":3},"a"]

and I would like to split these into two seperate lists, retaining the original order

[[ 'a', None,  'b', None, None,  'c'],
 [None,    1, None,    2,    3, None]]

or

[[{"A":1}, None, {"B":2},{"C":3}, None],
 [None,       1,    None,   None, None],
 [None,    None,    None,   None,  "a"]]

What I have :

def TypeSplit(sources)
  Types = [dict(),str(),num()]
  return [[item for item in sources if type(item) == type(itype)] for itype in types]  

Though this doesn’t fill in None.

The reason I’m doing this is that I will be given a list with different types of info and need to flesh it out with other values that compliment the original list.

Is there a better way to do this ?

Answer 1

This is a good use-case for the conditional expression. Also, I’m assuming you’d like to do this in as generalized a way as possible, so instead of using a fixed list of types, I’d suggest generating the list dynamically:

def type_split(sources):
    types = sorted(set(type(i) for i in sources))
    return [[item if type(item) == itype else None for item in sources] 
            for itype in types]  

If you need to use a fixed list (and you know that your input list won’t contain anything but those types and their subclasses), you could do this:

import collections
import numbers
def type_split(sources):
    types = [basestring, collections.Mapping, numbers.Number]
    return [[item if isinstance(item, itype) else None for item in sources] 
            for itype in types]