Nik.Birur - 4 months ago 17

Python Question

I am very new to Python and i am trying my best to learn Python. I have been trying to implement a community detection algorithm that i came across and i would really appreciate if i could get help from anyone here.

I have a **defaultdict(list)**, my input, which looks like :

`input = [('B', ['D']), ('D', ['E']), ('F', ['E']), ('G', ['D', 'F'])]`

Here,

I am trying to create a dictionary with

`output = [(('A', 'B'), 1.0), (('B', 'C'), 1.0), (('B', 'D'), 3.0), (('D', 'E'), 4.5), (('D', 'G'), 0.5), (('E', 'F'), 1.5), (('F', 'G'), 0.5)]`

In the above output, the key is a tuple which represents an edge in the input. For ex : ('A' , 'B') represents an edge between A and B and the int value is something that i calculate.

I would love to know know how this can be done.

I have tried the following:

1)

`edges = []`

for node,parents in input.items():

for p in sorted(parents):

tup = (node,p)

tup = sorted(tup)

edges.append(tup)

/*output of the above line: [['E', 'F'], ['D', 'E'], ['A', 'B'], ['B', 'C'], ['B', 'D'], ['D', 'G'], ['F', 'G']]*/

And then i thought i will pull values from this list to a dict. Obviously, i got a dict with

2)

`edges = {}`

for node,parents in node2parents.items():

for p in sorted(parents):

t = (node,p)

t = sorted(t)

edges[t] = 0

On executing the above, i got a

I have tried few other ways, but none proved to be successful. It would be great if someone could help me learn how i could do this.

PS : I would have posted evidences of more "failed" efforts of mine, but i dint want to waste your time by making you go through all the stupid ways i have been trying to accomplish my goals. Also, i googled and tried if i could find an answer to my question. Though there were countless possible solutions, i still failed to implement the logic successfully. I am honestly trying to learn Python and it would be great if you could push me in the right direction.

Answer

`sorted`

returns a new sorted `list`

, regardless of the input's type. If you want the result to be a sorted `tuple`

, just wrap the `sorted`

call in the `tuple`

constructor:

```
t = tuple(sorted(t))
```

For Python built-in types, only immutable types (e.g. `int`

, `str`

, or `tuple`

s and `frozenset`

s containing only other immutable types) are suitable for use as keys in `dict`

s and values in `set`

/`frozenset`

s, which is why preserving the `tuple`

type is important; `list`

is mutable, and to avoid a sticky situation where a mutable object like a `list`

is added to a `dict`

, then changed (so suddenly the hash and equality comparisons for it don't correspond to where it was bucketed), rendering it unfindable and violating the `dict`

assumptions, they prohibit using mutable built-in types completely.