subprocess : AttributeError: 'Popen' object has no attribute 'read'

[Peter Otten]

Mohan Mohta wrote:

> Hello,
> I am trying to grep the keyword (which I got from report_file ) from
> report_file
> 
> I tried multiple ways but am unable to get it to work.
> 
> Below are the methods I tried.
> 
> <Original Code>
> fp=open(txt_file,'r')
>      for line in fp :
>         line=line.strip()
>         var1=line.lower()
>         g_info=subprocess.Popen('cat report_file| grep -i '+var1,
>         stdout=subprocess.PIPE,stderr=subprocess.PIPE,shell=True)
>         g_info=g_info.read() g_info=g_info.strip()
>         info=g_info.strip('||')
>         print g_info
>         print info
> fp.close()

> Error:
> AttributeError: 'Popen' object has no attribute 'read'

You have to specify the stream/file, e. g. 

g_info.stdout.read() 

but when want both stdout and stderr your reading attempts may produce a 
deadlock as the fine manual warns.

So with basic error checks:

import subprocess

def grep(file, wanted):
    p = subprocess.Popen(
        ["grep", "-i", wanted, file],
        stdout=subprocess.PIPE, stderr=subprocess.PIPE
    )
    stdout, stderr = p.communicate()
    if p.returncode:
        raise Exception(stderr)
    return stdout


txt_file = "wanted.txt"
report_file = "report.txt"

with open(txt_file) as fp:
    for line in fp :
        wanted = line.strip().lower()
        print "Looking for:", wanted
        print "Found:"
        print grep(report_file, wanted)

>         info=g_info.strip('||')

This does not do what you think it does -- it will remove all "|" chars from 
the beginning and the end of the string, just like g_info.strip("|") and 
g_info.strip("||||||||||||||||") would, i. e. the str.strip() argument is 
treated like a set of chars.