如何从sys中得到前N行.在Python上逐行使用stdin

Question

我在为MapReduce编写减速器时遇到了一个问题。我想要得到非常大的文件的前10行，我使用了for循环和break。但是，break命令在hadoop上触发错误，所以我正在寻找另一种方法:

for line in fileinput.input():
    if(counter>limit):
        break
    line = line.strip()
    print (line)
    counter +=1

错误日志:

Error: java.io.IOException: subprocess exited successfully
R/W/S=6936/19/0 in:NA [rec/s] out:NA [rec/s]
minRecWrittenToEnableSkip_=9223372036854775807 HOST=null
USER=s2132211
HADOOP_USER=null
last tool output: |29670    YOU HAVE AATO|
Broken pipe
    at org.apache.hadoop.streaming.PipeReducer.reduce(PipeReducer.java:129)
    at org.apache.hadoop.mapred.ReduceTask.runOldReducer(ReduceTask.java:444)
    at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:392)
    at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:164)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:422)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1698)
    at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:158)

Answer 1

首先，要么您的示例格式不好，要么您有逻辑错误。print(line)和counter += 1应该是INSIDE for loop

更简单的写法是:

for counter, line in enumerate(fileinput.input()):
    if(counter>limit):
        break
    line = line.strip()
    print (line)

现在，如果这还不能解决问题，还有几个问题。

1)你能看到程序的任何输出(它实际上是从for循环打印的东西吗)?

2)程序是立即崩溃，还是在一段时间后崩溃?