采取加权平均用特定式

Question

infileName="grades.txt" 
infile=open(infileName,"r") 
outfileName="weightedavg.txt" 
outfile=open(outfileName,"w") 
for line in infile: 
    test=line.strip() 
    test=line.split() 
    fname=test[0] 
    lname=test[1] 
    grades=test[3::2] 
    weights=test[2::2] 
    grades=[int(i) for i in grades] 
    weights=[int(i) for i in grades] 
    weightedavg=???? 

用于加权平均的公式是（重量1 * grade1）+（重量2 * grade2）... +（+的Weightn园艺）

Answer 1

生成表达式（你能想到的一个隐含的列表理解的）可能是最“Python化”的解决方案：

grades = [83, 92, 96] 
weights = [0.4, 0.4, 0.2] 
weighted_avg = sum(x * y for x,y in zip(grades, weights)) 

最后，weighted_avg == 89.2

Answer 2

可以压缩这两个列表一起，乘每个对应的元素之和：

print(sum(a*b for a,b in zip(weights, grades))) 

这假定两个列表的长度相同，但我想他们还是你的逻辑是错误的。

我不知道我关注你的所有代码，你似乎循环，但不存储等级或权重的外循环，所以我想你想的每一行做到这一点：

infileName="grades.txt" 
outfileName="weightedavg.txt" 

with open(infileName) as infile, open(outfileName,"w") as outfile: 
    for line in infile: 
     test = line.split() 
     grades = map(int,test[3::2]) 
     weights = map(int,test[2::2]) 
     wghtd_avg = sum(a*b for a,b in zip(weights,grades)) 

如果你不”吨需要等级或权重比另做计算，你可以使用map与itertools.islice：

from itertools import islice 

with open(infileName) as infile, open(outfileName,"w") as outfile: 
    for line in infile: 
     test = line.split() 
     it = map(int, islice(test, 2, None)) # itertools.imap for python2 
     print(sum(a*b for a,b in zip(it, it))) 

使用with将自动关闭您的文件，使用itertools.imap和itertools.izip如果你正在使用python2。