Question

我试图在python脚本中读取（打开）和写入hdfs中的文件。但有错误。有人能告诉我这里有什么问题。

代码（完整）：sample.py

#!/usr/bin/python

from subprocess import Popen, PIPE

print "Before Loop"

cat = Popen(["hadoop", "fs", "-cat", "./sample.txt"],
            stdout=PIPE)

print "After Loop 1"
put = Popen(["hadoop", "fs", "-put", "-", "./modifiedfile.txt"],
            stdin=PIPE)

print "After Loop 2"
for line in cat.stdout:
    line += "Blah"
    print line
    print "Inside Loop"
    put.stdin.write(line)

cat.stdout.close()
cat.wait()
put.stdin.close()
put.wait()

执行时：

hadoop jar /usr/local/hadoop/share/hadoop/tools/lib/hadoop-streaming-2.5.1.jar -file ./sample.py -mapper './sample.py' -input sample.txt -output fileRead

它正确执行我找不到应该在hdfs modifiedfile中创建的文件

当我执行时：

 hadoop fs -getmerge ./fileRead/ file.txt

在file.txt中，我得到了：

Before Loop 
Before Loop 
After Loop 1    
After Loop 1    
After Loop 2    
After Loop 2

有人可以告诉我这里做错了什么吗？我不认为它从sample.txt中读取

Answer 1

尝试更改您的put子流程，通过更改此

来自行获取cat stdout

put = Popen(["hadoop", "fs", "-put", "-", "./modifiedfile.txt"],
            stdin=PIPE)

进入这个

put = Popen(["hadoop", "fs", "-put", "-", "./modifiedfile.txt"],
            stdin=cat.stdout)

完整脚本：

#!/usr/bin/python

from subprocess import Popen, PIPE

print "Before Loop"

cat = Popen(["hadoop", "fs", "-cat", "./sample.txt"],
            stdout=PIPE)

print "After Loop 1"
put = Popen(["hadoop", "fs", "-put", "-", "./modifiedfile.txt"],
            stdin=cat.stdout)
put.communicate()

Answer 2

有人可以告诉我这里我做错了吗？

您的sample.py可能不是合适的映射器。映射器可能接受其在stdin上的输入并将结果写入其标准输出，例如blah.py：

#!/usr/bin/env python
import sys

for line in sys.stdin: # print("Blah\n".join(sys.stdin) + "Blah\n")
    line += "Blah"
    print(line)

用法：

$ hadoop ... -file ./blah.py -mapper './blah.py' -input sample.txt -output fileRead

使用python和subprocess，Pipe，Popen从hdfs读取/写入文件会出错

2 个答案: