python map和reduce的用法
python map和reduce的用法
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map(function,sequence[,sequence,...]) -> list
Return a list of the results of applying the function to the items of
the argument sequence(s).If more than one sequence is given,the
function is called with an argument list consisting of the corresponding
item of each sequence,substituting None for missing values when not all
sequences have the same length.If the function is None,return a list of
the items of the sequence (or a list of tuples if more than one sequence).
reduce(...)
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.