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How to run python code in the currently activated virtualenv with subprocess?

I have a virtualenv named 'venv' and it is activate:
(venv)>
and I wrote codes that I'll run it in the virtualenv (main.py):
import subprocess
result = subprocess.run('python other.py', stdout=subprocess.PIPE)
but when I run main.py file:
(venv)> python main.py
subprocess does not execute the command (python other.py) in the virtualenv i.e venv
How to run subprocess command in the current virtualenv session?

A child process can't run commands in its parent process without that process's involvement.
This is why ssh-agent requires usage as eval "$(ssh-agent -s)" to invoke the shell commands it emits on output, for example. Thus, the literal thing you're asking for here is impossible.
Fortunately, it's also unnecessary.
virtualenvs use environment variables inherited by child processes.
This means that you don't actually need to use the same shell that has a virtualenv activated to start a new Python interpreter intended to use the interpreter/libraries/etc. from that virtualenv.
subprocess.run must be passed a list, or shell=True must be used.
Either do this (which is better!)
import subprocess
result = subprocess.run(['python', 'other.py'], stdout=subprocess.PIPE)
Or this (which is worse!)
import subprocess
result = subprocess.run('python other.py', stdout=subprocess.PIPE, shell=True)

If you want to run a script with the same Python executable being used to run the current script, don't use python and rely on the path being set up properly, just use sys.executable:
A string giving the absolute path of the executable binary for the Python interpreter, on systems where this makes sense.
This works if you executed the script with python myscript.py relying on the active virtualenv's PATH. It also works if you executed the script with /usr/local/bin/python3.6 to ignore the PATH and test your script with a specific interpreter. Or if you executed the script with myscript.py, relying on a shbang line created at installation time by setuptools. Or if the script was run as a CGI depending on your Apache configuration. Or if you sudod the executable, or did something else that scraped down your environment. Or almost anything else imaginable.1
As explained in Charles Duffy's answer, you still need to use a list of arguments instead of a string (or use shell=True, but you rarely want to do that). So:
result = subprocess.run([sys.executable, 'other.py'], stdout=subprocess.PIPE)
1. Well, not quite… Examples of where it doesn't work include custom C programs that embed a CPython interpreter, some smartphone mini-Python environments, old-school Amiga Python, … The one most likely to affect you—and it's a pretty big stretch—is that on some *nix platforms, if you write a program that execs Python by passing incompatible names for the process and arg0, sys.executable can end up wrong.

Executing a python script from the terminal in Unix

I have a python script and I can't figure how to execute it in the terminal. The script has the #!/usr/bin/python at the beginning, is executable and I've tried locating myself in the right directory and python name.py but what I want to print (ergo what the script says it should print) doesn't print in the terminal.
I feel I'm missing something... I just started with this so... Help!

If name.py is executable, you can run it using:
./name.py
As for the #!, it is better to use as a first line:
#!/usr/bin/env python
This way path to python interpreter is not hardcoded, the first python found in $PATH is used instead.
Also: it makes your script to run in fresh environment (you can see man env for more information).

Executing some simple command in Command prompt using Python

I need to execute the simple command below in windows 7 command prompt using Python26.
cd C:\Python26\main project files\Process
C:\Aster\runtime\waster Analysis.comm
It runs a FEM simulation and I tried it manually and it worked well. Now, I want to automate the write procedure using Python26.
I studied the other questions and found that the os.system works but it didn't. Also I saw subprocess module but it didn't work.

The current directory is a process property: Every single process has its own current directory. A line like
os.system("cd xyz")
starts a command interpreter (cmd.exe on Windows 7) and execute the cd command in this subprocess, not affecting the calling process in any way. To change the directory of the calling process, you can use os.chdir() or the cwd keyword parameter to subprocess.Popen().
Example code:
p = subproces.Popen(["C:/Aster/runtime/waster", "Analysis.comm"],
cwd="C:/Python26/main project files/Process")
p.wait()
(Side notes: Use forward slashes in path names in Python files. You should avoid os.system() and passing shell=True to the function in the subprocess module unless really necessary.)

Run python source file from PowerShell

I'm trying to learn python but have some problem running source files from power shell. When I type 'python' it opens up and I can type python commands directly in the shell. I think this is called interactive mode. But when I try to run/execute a source file I get an error message: It sayys: Syntax error: invalid syntax.
I use 'python myfile.py' when I try to execute the script.
If I run the same file from IDLE it works just fine. Ana idea what I'm doing wrong?
Here is myfile.py. I'm running python 2.7
# filename: myfile.py
while True:
s = raw_input('Enter something: ')
if s == 'Quit':
break
print 'Lenght of the string is', len(s)
print 'Done'

You might have more than one version of Python installed and the version IDLE is using is newer. To see what version of python you have you can type >python -V at a command line. If that version looks appropriate then you might need the full path to the file as the second parameter. E.g >python C:\myfile.py.
If you installed Python correctly there is always a chance that just typing the name of the script will run it with python. E.g. >myfile.py
I always find that adding C:\Python27 to the %PATH% variable and .PY to the %PATHEXT% variable makes running scripts easier. In this case just >myfile should work.
Edit after Update:
Typing just >python with no parameters opens python in 'interactive mode' which is different from the batch or scripting mode that your script is intended for. If executed with arguments the first argument is taken as the file path and further arguments are passed to the script in the sys.argv list.

You will need to put the full path of the Python executable within the command line in order for it to work. You could check and ensure that your python exe is included in your Path among your system variables.

Disclaimer: I don't know PowerShell, but I do know cmd.exe.
I don't know why python myfile.py doesn't work, but assuming that PowerShell bears at least some similarity to cmd.exe, the following should probably work: myfile.py. That's right, just enter the name of the Python script and hit enter.

If you started by typing "python" in powershell you will need to get out of that script.
If you are in python type:
quit()
then type
python myfile.py
This should work if your python is installed correctly.

Try to type this in Powershell:
$env:path="$env:Path;C:\Python33
After this, command
python yourfile.py
should work.

This my sound silly, especially coming from a beginner.
Just save the file on your desktop. Open up powershell and drag the file directly into powershell and it opens. kind of tedious but it works

trying to call a perl script from python, resulting in weird behaviour

I am trying to call a perl script from my python program with the following line:
subprocess.call(r'/path/to/compute_lexrank.pl /path/to/11sent',shell=True)
when I run the same perl script from the shell (just typing /path/to/compute_lexrank.pl /path/to/11sent) it works fine as expected, but when I run it from the python program, the perl script is executed, but gives a mysterious error:
Math::MatrixReal::new(): number of rows must be integer > 0 at /Users/filippo/Downloads/clairlib-core-1.08/lib//Clair/Network.pm line 1628
now because I havent wrote the perl script myself I dont know how to fix this, but why the same script behaves differently when I run it from the shell or from subprocess.call?
I am using MacOsX, python 2.6 (but I have tried also with 2.5, same stuff) and perl 5.10.
Anyone can help?

In Perl, there's a good rule: if possible, use list forms of popen and system. Python seems to have those, too. I wonder what happens if you try this out:
helper = "/path/to/compute_lexrank.pl"
helper_input = "/path/to/11sent"
subprocess.call([helper, helper_input])

You may need to pass the working directory to the subprocess.call
subprocess.call(r'/path/to/compute_lexrank.pl /path/to/11sent',shell=True,cwd="/path/to")
If cwd is not None, the child’s current directory will be changed to cwd before it is executed. Note that this directory is not considered when searching the executable, so you can’t specify the program’s path relative to cwd.