從一個迭代器創建兩個字典

Question

我需要在從一個生成器讀取輸入的同時創建兩個字典。我很關心dict和數據原則上只需要滾動一次的事實。我應該如何繼續？

# dummy data 
def data(): 
    yield 'a', 5 
    yield 'b', 8 
    yield 'c', 12 

# two iterations, bad. 
first = {k: v + 1 for k, v in data()} 
second = {k: 2 * v for k, v in data()} 

# One iteration only, but it scans both dicts on each step? 
first = {} 
second = {} 
for k, v in data(): 
    first[k] = v # this needs an underlying iteration over `first`, right? 
    second[k] = v # and this needs another underlying iteration over `second`.. 

# Is there aa.. multiple comprehension? 
first, second = {k: v + 1, k: 2 * v for k, v in data()} # SyntaxError 
# Would it be just equivalent to the previous loop? 

Answer 1

你的第二個做法可能是最好的方式，加入一鍵一dict並不需要在這dict底層迭代。事實上，它的時間複雜度簡單地爲O（1），即恆定時間，並且與字典大小無關。