Python subprocess.Popen() error (No such file or directory)

Question

I am trying to count the number of lines in a file using Python functions. Within the current directory, while os.system("ls") finds the file, the command subprocess.Popen(["wc -l filename"], stdout=subprocess.PIPE) does not work.

Here is my code:

>>> import os >>> import subprocess >>> os.system("ls") sorted_list.dat 0 >>> p = subprocess.Popen(["wc -l sorted_list.dat"], stdout=subprocess.PIPE)File "<stdin>", line 1, in <module> File "/Users/a200/anaconda/lib/python2.7/subprocess.py", line 710, in __init__     errread, errwrite) File "/Users/a200/anaconda/lib/python2.7/subprocess.py", line 1335, in _execute_child     raise child_exception OSError: [Errno 2] No such file or directory 

Answer 1

You should pass the arguments as a list (recommended):

subprocess.Popen(["wc", "-l", "sorted_list.dat"], stdout=subprocess.PIPE) 

Otherwise, you need to pass shell=True if you want to use the whole "wc -l sorted_list.dat" string as a command (not recommended, can be a security hazard).

subprocess.Popen("wc -l sorted_list.dat", shell=True, stdout=subprocess.PIPE) 

Read more about shell=True security issues here.

Answer 2

The error occurs because you are trying to run a command named wc -l sorted_list.dat, that is, it is trying to find a file named like "/usr/bin/wc -l sorted dat".

Split your arguments:

["wc", "-l", "sorted_list.dat"]