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Puzzle 19: Explanation

Puzzle 19: Explanation

Let’s find out how mutable default arguments work in Python.

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Python 3.8
import re
from collections import defaultdict
def word_freq(text, freqs=defaultdict(int)): 
    """Calculate word frequency in text. freqs are previous frequencies"""
    for word in [w.lower() for w in re.findall(r'\w+', text)]:
        freqs[word] += 1
    return freqs
freqs1 = word_freq('Duck season. Duck!')
freqs2 = word_freq('Rabbit season. Rabbit!')
print(freqs1)
print(freqs2)

Explanation

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