按ctrl + D不會給出完整的輸出

Question

我在python中有以下代碼：

#!/usr/bin/python

import sys

def reducer():

    oldKey = None
    totalSales = 0

    for line in sys.stdin:
            data= line.strip().split("\t")
            if(len(data)!=2):
                    continue

            thisKey,thisSale = data

            if (oldKey and oldKey != thisKey):
                    print ("{}\t{}".format(oldKey,totalSales))
                    oldKey=thisKey
                    totalSales = 0


            oldKey = thisKey
            totalSales += float(thisSale)

    if(oldKey!=None):
            print("{}\t{}".format(oldKey,totalSales))

reducer()

當我給出輸入時：

a       1
a       2
a       3
b       4
b       5
b       6
c       1
c       2

並在此處按Ctrl + D.

我得到輸出：

a       6.0
b       15.0

我期望輸出為：

a       6.0
b       15.0
c       3.0

我再次按Ctrl + D后才能獲得完整輸出。 為什么會這樣？ 我該如何解決？

Answer 1

文件對象迭代（ for line in sys.stdin: .. ）執行內部緩沖會導致您觀察到的行為。

通過在while循環中使用sys.stdin.readline() ，可以避免它。

更改以下行：

for line in sys.stdin:

有：

while True:
    line = sys.stdin.readline()
    if not line:
        break

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相關PYTHON（1）聯機頁面部分：

  -u Force stdin, stdout and stderr to be totally unbuffered. On systems where it matters, also put stdin, stdout and stderr in binary mode. Note that there is internal buffering in xread‐ lines(), readlines() and file-object iterators ("for line in sys.stdin") which is not influenced by this option. To work around this, you will want to use "sys.stdin.readline()" inside a "while 1:" loop.