I have this dictionary. 

```
d = {'match1': {'player1': 57, 'player2': 38},
     'match2': {'player1': 42, 'player3': 9},
     'match3': {'player2': 41, 'player3': 91, 'player4': 63}}

```

I want a loop to run with index `player1, player2, player3, player4.` 
How do I write the loop structure? There might be many more **players**.

I tried:

```
for i in ["player1", "player2", "player3", "player4"]:

```

But this only works for exactly 4 players. What to do if players are more or less?