passing sentence as a argument in subprocess command

Question

I am executing python script inside another script and want to pass two arguments to it

lines = [line.strip('\n') for line in open('que.txt')]
for l in lines:
    print 'my sentence : '
    print l
    #os.system("find_entity.py")  //this also does not work
    subprocess.call(" python find_entity.py l 1", shell=True) //this works but l does not considered as sentence which was read

what is the correct approach?

update:

lines = [line.strip('\n') for line in open('q0.txt')]
for line_num, line in enumerate(lines):
    cmd = ["python", "find_entity.py", line]
    subprocess.call(cmd, shell=True)

then it goes to python terminal

Answer 1

You can use one of string substitution mechanics:

• C-style string formatting

  in your case it would looks like

   subprocess.call("python find_entity.py %s %d" % (line, line_num)) 

• C#-style string formatting

   subprocess.call("python find_entity.py {} {}".format(line, line_num)) 

• or templates

Or, in case with subprocess library you should pass arguments as list to call function:

subprocess.call(["python", "find_entity.py", line, str(line_num)])

Look at line and line_num variables — they pass without any quotes, so they would be passed by value. This solution is recommended, because it provides more clean and obvious code and provide correct parameter's processing(such as whitespace escaping, etc).

However, if you want to use shell=True flag for subprocess.call , solution with list of args will not work instead of string substitution solutions. BTW, subprocess and os provides all shell powerful options: such as script piping, expanding user home directory(~), etc. So, if you will code big and complicated script you should use python libraries instead of using shell=True .

Answer 2

you need the contents of variable l (I renamed it to line), not the string literal "l"

for line_num, line in enumerate(lines):
    cmd = ["python",
           "find_entity.py",
           line,
           str(line_num)]
    subprocess.call(cmd, shell=True)

Answer 3

If you already have the command name and its arguments in separate variables, or already in a list, you almost never want to use shell=True . (It's not illegal, but its behavior is undocumented and generally not what is wanted.)

cmd = ["python", "find_entity.py", line]
subprocess.call(cmd)