Question: I have a large list like:

```
[A][B1][C1]=1
[A][B1][C2]=2
[A][B2]=3
[D][E][F][G]=4

```

I want to build a multi-level dict like:

```
A
--B1
-----C1=1
-----C2=1
--B2=3
D
--E
----F
------G=4

```

I know that if I use recursive defaultdict I can write `table[A][B1][C1]=1`, `table[A][B2]=2`, but this works only if I hardcode those insert statement. 

While parsing the list, I don't how many []'s I need beforehand to call `table[key1][key2][...]`.

Answer: 
You can do it without even defining a class:

```
from collections import defaultdict

nested_dict = lambda: defaultdict(nested_dict)
nest = nested_dict()

nest[0][1][2][3][4][5] = 6

```
Your example says that at any level there can be a value, and also a dictionary of sub-elements. That is called a **tree**, and there are many implementations available for them. This is one:

```
from collections import defaultdict
class Tree(defaultdict):
    def __init__(self, value=None):
        super(Tree, self).__init__(Tree)
        self.value = value

root = Tree()
root.value = 1
root['a']['b'].value = 3
print root.value
print root['a']['b'].value
print root['c']['d']['f'].value

```

Outputs:

```
1
3
None

```

You could do something similar by writing the input in JSON and using `json.load` to read it as a structure of nested dictionaries.