i want to extract the keys from dict of string column “C”. keys will be different in all rows

df3 = pl.DataFrame({
   "A": ["a", "b", "a", "c","a","c","a","b","b"], 
   "B": [23,45,60,50,56,44,34,30,97], 
   "C": ["{'pattern1':['a','score1'],'pattern2':['df','text1']}",
        "{'pattern3':['abc','score1']}",
        "{'pattern1':['a','score2'],'pattern4':['df','text2']}",
        "{'pattern5':['a','score2'],'pattern6':['gh','text1'],'pattern7':['gh','text1']}",
        "{'pattern8':['a','score1']}",
        "{'pattern9':['a','score1'],'pattern10':['df','text1']}",
        "{'pattern11':['a','score1']}",
        "{'pattern12':['a','score1'],'pattern13':['df','text1']}",
        "{'pattern3':['a','score1'],'pattern5':['df','text1']}"]
})

need to extract the keys from string column “C” which is dict .

shape: (9, 4)
┌─────┬─────┬───────────────────────────────────────────────────────────────────┬──────────────────────────────────────┐
│ A   ┆ B   ┆ C                                                                 ┆ KEYS                                 │
│ --- ┆ --- ┆ ---                                                               ┆ ---                                  │
│ str ┆ i64 ┆ str                                                               ┆ list[str]                            │
╞═════╪═════╪═══════════════════════════════════════════════════════════════════╪══════════════════════════════════════╡
│ a   ┆ 23  ┆ {'pattern1':['a','score1'],'pattern2':['df','text1']}             ┆ ["pattern1", "pattern2"]             │
│ b   ┆ 45  ┆ {'pattern3':['abc','score1']}                                     ┆ ["pattern3"]                         │
│ a   ┆ 60  ┆ {'pattern1':['a','score2'],'pattern4':['df','text2']}             ┆ ["pattern1", "pattern4"]             │
│ c   ┆ 50  ┆ {'pattern5':['a','score2'],'pattern6':['gh','text1'],'pattern7':[ ┆ ["pattern5", "pattern6", "pattern7"] │
│     ┆     ┆ 'gh','text1']}                                                    ┆                                      │
│ a   ┆ 56  ┆ {'pattern8':['a','score1']}                                       ┆ ["pattern8"]                         │
│ c   ┆ 44  ┆ {'pattern9':['a','score1'],'pattern10':['df','text1']}            ┆ ["pattern9", "pattern10"]            │
│ a   ┆ 34  ┆ {'pattern11':['a','score1']}                                      ┆ ["pattern11"]                        │
│ b   ┆ 30  ┆ {'pattern12':['a','score1'],'pattern13':['df','text1']}           ┆ ["pattern12", "pattern13"]           │
│ b   ┆ 97  ┆ {'pattern3':['a','score1'],'pattern5':['df','text1']}             ┆ ["pattern3", "pattern5"]             │
└─────┴─────┴───────────────────────────────────────────────────────────────────┴──────────────────────────────────────┘