Question

今天我尝试在Linux中执行以下命令，我想测试hadoop中的Streaming接口，

 cat test.txt|php wc_mapper.php|python Reducer.py

发生错误：

"Traceback (most recent call last):
 File "Reducer.py", line 7, in <module>
word,count = line.split()   
ValueError: need more than 0 values to unpack
"

test.txt的内容如下：

hello world
hello world
hello world

由PHP编写的wc_mapper.php的内容是

#!/usr/bin/php
<?php
error_reporting(E_ALL ^ E_NOTICE);
$word2count = array();
while (($line = fgets(STDIN)) !== false) {
      $line = trim($line);
      $words = preg_split('/\W/', $line, 0, PREG_SPLIT_NO_EMPTY);
      foreach ($words as $word) {
                echo $word, chr(9), "1", PHP_EOL;
      }
}
?>

并且Python编写的Reducer.py的内容是

#!/usr/bin/python
from operator import itemgetter
import sys
word2count = {}
for line in sys.stdin:
   line = line.strip()
   word,count = line.split()
   try:
      count = int(count)
      word2count[word] = word2count.get(word, 0) + count
   except ValueError:
      pass

sorted_word2count = sorted(word2count.items(), key=itemgetter(0))
for word,count in sorted_word2count:
   print '%s\t%s'%(word,count)

谁知道错误的原因，如何解决这个问题？当我执行第一部分命令

时

cat test.txt|php wc_mapper.php|sort

，我得到了以下输出：

hello   1
hello   1
hello   1
world   1
world   1
world   1

第一行为null，但占用一行。

Answer 1

在split()函数

中提供分隔符

   try:    
        word,count = line.split(" ") 
   except:
        print("Error")

我已将单个空格作为分隔符。你可以改变。

ValueError：需要超过0个值来解压缩Python中的错误

1 个答案: