Saving return value of subprocess.Popen to a global variable

Question

Is it possible to save or store the return value of a subprocess.Popen() to a global variable? For example,

global_var = none
 ...
 def some_function():
    p = subprocess.Popen(...,stdout=subprocess.PIPE, shell=True)
    global_var = p

 def some_function_2():
    x = global_var.stdout

Something like this. I'm essentially trying to read output from a subprocess that is started earlier in code but I need to begin the read later on.

what happens when you do this? what do you expect to happen? Comparing actual behavior to expected behavior is crucial in determining how others can help. — JacobIRR, Jun 19 '18 at 01:05
There is nothing special about global variables. Any variable declared at the outermost level of indentation is global. If you simply write `p = subprocess.Popen(...)`, outside of any function or class definition, p will be a global variable. So the Popen object, like any other, can be stored anywhere. — Paul Cornelius, Jun 19 '18 at 01:06
@JacobIRR, so performing x = global_var.stdout does not work since the value of global_var.stdout is None for whatever reason and not the file object returned from subprocess.Popen. — Chris, Jun 19 '18 at 01:12

score 2 · Answer 1 · answered Jun 19 '18 at 01:18

So this ended up being a silly oversight. All I needed to do was call global and the global variable name inside the function to set its value correctly like so:

global_var = none
 ...
 def some_function():
    p = subprocess.Popen(...,stdout=subprocess.PIPE, shell=True)
    global global_var
    global_var = p

 def some_function_2():
    x = global_var.stdout

score 1 · Answer 2 · answered Jun 19 '18 at 01:25

You need to add one line to some_function. I also give a better solution.

 global_var = None  
 ...
 def some_function():
    global global_var # without this line, Python will create a local named global_variable
    p = subprocess.Popen(...,stdout=subprocess.PIPE, shell=True)
    global_var = p

 def some_function_2():
    x = global_var.stdout

Better is:

 def some_function():
    # I assume this function does some other things, otherwise
    # you don't need to write a function to just call another.
    p = subprocess.Popen(...,stdout=subprocess.PIPE, shell=
    return p

 my_process = some_function()

 def some_function_2():
    x = my_process.stdout

Saving return value of subprocess.Popen to a global variable

2 Answers2