Python – how do I call external python programs?
Question:
I’ll preface this by saying it’s a homework assignment. I don’t want code written out for me, just to be pointed in the right direction.
We’re able to work on a project of our choice so I’m working on a program to be a mini portfolio of everything I’ve written so far. So I’m going to make a program that the user will input the name of a program (chosen from a given list) and then run the chosen program within the existing shell.
However, I can’t really find information on how to call upon external programs. Can anyone point me in the right direction? I considered putting all the code in one long program with a bunch of if loops to execute the right code, but I’d like to make it a BIT more complicated than that.
Answers:
Check out the subprocess documentation.
If you want to call each as a Python script, you can do
import subprocess
subprocess.call(["python", "myscript.py"])
subprocess.call(["python", "myscript2.py"])
But a better way is to call functions you’ve written in other scripts, like this:
import myscript
import myscript2
myscript.function_from_script1()
myscript2.function_from_script2()
Where function_from_script1() etc are defined in the myscript.py and myscript2.py files. See this page on modules for more information.
Also if you need to pass additional arguments do this:
import subprocess
subprocess.call(["python", "myscript.py", "arg1", "arg2", "argN"])
If you want to load an external Python file and run it inside the current interpreter without the burden to dealing with modules, you can use the standard importlib.util module.
This is useful when you need to ship some Python scripts for demonstration purposes, but you don’t want to make them part of a (sub-)module–while still being able to run them automatically, like during integration testing. Here is an example:
# A sample Python script
sh$ cat snippet/demo.py
SOME_MODULE_GLOBAL=True
print("Hello, here is the demo snippet!")
# There is no `__init__.py in the _snippet_ directory
sh$ cat snippet/__init__.py
cat: snippet/__init__.py: No such file or directory
Now using importlib.util you can load demo.py even if it is not part of a module:
>>> import importlib.util
# Bypass the standard import machinery to manually load a Python script from
# a filepath
>>> spec = importlib.util.spec_from_file_location('demo','snippet/demo.py')
>>> spec
ModuleSpec(name='demo', loader=<_frozen_importlib_external.SourceFileLoader object at 0x7fa549344eb8>, origin='snippet/demo.py')
>>> module = importlib.util.module_from_spec(spec)
>>> module
<module 'demo' from 'snippet/demo.py'>
# The next command will run the module:
>>> spec.loader.exec_module(module)
Hello, here is the demo snippet!
# Module variables are accessible just like if it was a
# _normally_ imported module:
>>> module.SOME_MODULE_GLOBAL
True
I’ll preface this by saying it’s a homework assignment. I don’t want code written out for me, just to be pointed in the right direction.
We’re able to work on a project of our choice so I’m working on a program to be a mini portfolio of everything I’ve written so far. So I’m going to make a program that the user will input the name of a program (chosen from a given list) and then run the chosen program within the existing shell.
However, I can’t really find information on how to call upon external programs. Can anyone point me in the right direction? I considered putting all the code in one long program with a bunch of if loops to execute the right code, but I’d like to make it a BIT more complicated than that.
Check out the subprocess documentation.
If you want to call each as a Python script, you can do
import subprocess
subprocess.call(["python", "myscript.py"])
subprocess.call(["python", "myscript2.py"])
But a better way is to call functions you’ve written in other scripts, like this:
import myscript
import myscript2
myscript.function_from_script1()
myscript2.function_from_script2()
Where function_from_script1() etc are defined in the myscript.py and myscript2.py files. See this page on modules for more information.
Also if you need to pass additional arguments do this:
import subprocess
subprocess.call(["python", "myscript.py", "arg1", "arg2", "argN"])
If you want to load an external Python file and run it inside the current interpreter without the burden to dealing with modules, you can use the standard importlib.util module.
This is useful when you need to ship some Python scripts for demonstration purposes, but you don’t want to make them part of a (sub-)module–while still being able to run them automatically, like during integration testing. Here is an example:
# A sample Python script
sh$ cat snippet/demo.py
SOME_MODULE_GLOBAL=True
print("Hello, here is the demo snippet!")
# There is no `__init__.py in the _snippet_ directory
sh$ cat snippet/__init__.py
cat: snippet/__init__.py: No such file or directory
Now using importlib.util you can load demo.py even if it is not part of a module:
>>> import importlib.util
# Bypass the standard import machinery to manually load a Python script from
# a filepath
>>> spec = importlib.util.spec_from_file_location('demo','snippet/demo.py')
>>> spec
ModuleSpec(name='demo', loader=<_frozen_importlib_external.SourceFileLoader object at 0x7fa549344eb8>, origin='snippet/demo.py')
>>> module = importlib.util.module_from_spec(spec)
>>> module
<module 'demo' from 'snippet/demo.py'>
# The next command will run the module:
>>> spec.loader.exec_module(module)
Hello, here is the demo snippet!
# Module variables are accessible just like if it was a
# _normally_ imported module:
>>> module.SOME_MODULE_GLOBAL
True