為什么這里的reduce 函數需要加上第三個參數？

def calc_prod(lst):
??? def lazy_prod():
?????? def f(x,y):
?????????? return x*y
??????? return reduce(f,1st,1)
??????? #return reduce(f,1st)
??? return lazy_prod

f = calc_prod([1, 2, 3, 4])
print f()

青木河

2015-04-07

源自：python進階 2-8

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1 回答

DanDanHang
2015-04-13

reduce(function,?sequence[,?initial])?->?value

Apply?a?function?of?two?arguments?cumulatively?to?the?items?of?a?sequence,
from?left?to?right,?so?as?to?reduce?the?sequence?to?a?single?value.
For?example,?reduce(lambda?x,?y:?x+y,?[1,?2,?3,?4,?5])?calculates
((((1+2)+3)+4)+5).??If?initial?is?present,?it?is?placed?before?the?items
of?the?sequence?in?the?calculation,?and?serves?as?a?default?when?the
sequence?is?empty.

自己解讀下這句話，應該對你有幫助 If initial is present, it is placed before the items?of the sequence in the calculation, and serves as a default when the?sequence is empty.?