import pandas as pd
df = pd.DataFrame({'TMEDIA C': {17054: '16',
17055: '15',
17056: '15',
17057: '19',
17058: '17',
17059: '18',
17060: '19',
17061: '20',
17062: '21',
17063: '20'}})
print(df['TMEDIA C'].str.replace(',','.').astype(float))
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