Tutorial :Popen and python



Question:

Working on some code and I'm given the error when running it from the command prompt...

NameError: name 'Popen' is not defined  

but I've imported both import os and import sys.

Here's part of the code

exepath = os.path.join(EXE File location is here)  exepath = '"' + os.path.normpath(exepath) + '"'  cmd = [exepath, '-el', str(el), '-n', str(z)]    print 'The python program is running this command:'  print cmd    process = Popen(cmd, stderr=STDOUT, stdout=PIPE)  outputstring = process.communicate()[0]  

Am I missing something elementary? I wouldn't doubt it. Thanks!


Solution:1

you should do:

import subprocess  subprocess.Popen(cmd, stderr=subprocess.STDOUT, stdout=subprocess.PIPE)  # etc.  


Solution:2

Popen is defined in the subprocess module

import subprocess  ...  subprocess.Popen(...)  

Or:

from subprocess import Popen  Popen(...)  


Solution:3

When you import a module, the module's members don't become part of the global namespace: you still have to prefix them with modulename.. So, you have to say

import os  process = os.popen(command, mode, bufsize)  

Alternatively, you can use the from module import names syntax to import things into the global namespace:

from os import popen    # Or, from os import * to import everything  process = popen(command, mode, bufsize)  


Solution:4

This looks like Popen from the subprocess module (python >= 2.4)

from subprocess import Popen  


Solution:5

If your import looks like this:

import os  

Then you need to reference the things included in os like this:

os.popen()  

If you dont want to do that, you can change your import to look like this:

from os import *  

Which is not recommended because it can lead to namespace ambiguities (things in your code conflicting with things imported elsewhere.) You could also just do:

from os import popen  

Which is more explicit and easier to read than from os import *


Solution:6

You should be using os.popen() if you simply import os.


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