Paring Down a Dictionary of Lists in Python

Question

I'm working with a dictionary for an anagram program in Python. The keys are tuples of sorted letters, and the values are arrays of the possible words with those letters: ``` wordlist = { ('d', 'g', 'o'): ['dog', 'god'], ('a', 'c', 't'): ['act', 'cat'], ('a', 's', 't'): ['sat', 'tas'], } ``` I am using regex to filter the list down. So given `r't$'` as a filter the final result should be: ``` filtered_list = { ('a', 'c', 't'): ['act', 'cat'], ('a', 's', 't'): ['sat'], } ``` So far I've gotten it down to two steps. First, keep all of the words that match the expression: ``` tmp = {k: [w for w in v if re.search(r't$', w)] for k, v in wordlist.items()} ``` This leaves me with empty lists: ``` { ('d', 'g', 'o'): [], ('a', 'c', 't'): ['act', 'cat'], ('a', 's', 't'): ['sat'], } ``` Then I need a second pass to get rid of the empty lists: ``` filtered_list = {k: v for k, v in tmp.items() if v} ``` I'm sure there is a way to do these in one step, but I haven't figured it out yet. Is there a w…

Accepted Answer

Doing this in two steps is fine, and probably good for readability.

But to answer your question, here's a one-liner (broken into multiple lines, for readability). It uses a generator expression for generating the pairs from the first step.

```
{
  k:v for k, v in
  (
    (kk, [w for w in vv if re.search(r't$', w)])
    for kk, vv in wordlist.items()
  )
  if v
}
=> {('a', 'c', 't'): ['act', 'cat'], ('a', 's', 't'): ['sat']}
```

Paring Down a Dictionary of Lists in Python

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