I have a list as follows
['item1', 'item2', 'item3', 'item4'] I want to construct a dictionary from the above list as follows
{ "item1": { "item2": { "item3": "item4" } } } The number of items in the list is dynamic. The dictionary will be a nested dictionary till it reaches the last element of the list. Is there any way in python to do this?
Simple one-liner:
a = ['item1', 'item2', 'item3','item4'] print reduce(lambda x, y: {y: x}, reversed(a)) For better understanding the above code can be expanded to:
def nest_me(x, y): """ Take two arguments and return a one element dict with first argument as a value and second as a key """ return {y: x} a = ['item1', 'item2', 'item3','item4'] rev_a = reversed(a) # ['item4', 'item3', 'item2','item1'] print reduce( nest_me, # Function applied until the list is reduced to one element list rev_a # Iterable to be reduced ) # {'item1': {'item2': {'item3': 'item4'}}} Use recursion:
In [10]: src = ['item1', 'item2', 'item3','item4'] In [11]: def list2dict(src_list): if len(src_list) > 1: return {src_list[0] : list2dict(src_list[1:])} else: return src_list[0] ....: In [12]: In [12]: list2dict(src) Out[12]: {'item1': {'item2': {'item3': 'item4'}}} Using the reduce() function to access and set elements:
try: # Python 3 moved reduce to the functools module from functools import reduce except ImportError: # Python 2 reduce is a built-in pass def get_target(d, keys): return reduce(lambda d, k: d.setdefault(k, {}), keys, d) def set_target(d, keys, value): parent = get_target(d, keys[:-1]) parent[keys[-1]] = value result = {} set_target(result, yourlist[:-1], yourlist[-1]) The get_target() and set_target() functions are re-usable on already-built nested structures, they are not limited to building a dictionary from scratch. I adapted get_target() from an earlier, related post.
Demo:
>>> def get_target(d, keys): ... return reduce(lambda d, k: d.setdefault(k, {}), keys, d) ... >>> def set_target(d, keys, value): ... parent = get_target(d, keys[:-1]) ... parent[keys[-1]] = value ... >>> result = {} >>> yourlist = ['item1', 'item2', 'item3', 'item4'] >>> set_target(result, yourlist[:-1], yourlist[-1]) >>> result {'item1': {'item2': {'item3': 'item4'}}}