Python run program by name

Python Project — Command Line

In the following examples, all the modules are executed from the project’s root directory (top-level package). This is important since the root dir has access to all the packages (sub-directories) in the project.

Executing the main.py script and appy as a module with src/appy/__main__.py

# Executing as a script - works as long as there are no relative imports of parent packages (python-project) $ python main.py My Path: python-project/main.py Created the file: /Users/meirgabay/python-project/meirg-ascii.txt Insert your name: willy wonka Hello Willy Wonka, here's the cat fact of the day: Jaguars are the only big cats that don't roar. # Executing as a module - works because of the __main__.py file (python-project) $ python -m src.appy My Path: python-project/src/appy/__main__.py Created the file: /Users/meirgabay/python-project/meirg-ascii.txt Insert your name: willy wonka Hello Willy Wonka, here's the cat fact of the day: A cat has more bones than a human being; humans have 206 and the cat has 230 bones. 

Executing the module src/appy/core/app.py from the root directory

# Contains relative imports - `..utils.message` # Excuting as a script - causes issues with relative imports of parent packages (python-project) $ python src/appy/core/app.py Traceback (most recent call last): File "src/appy/core/app.py", line 1, in from ..utils import message, img_ascii ImportError: attempted relative import with no known parent package # Excuting as a module - works perfect with relative imports (python-project) $ python -m src.appy.core.app My Path: python-project/src/appy/core/app.py Created the file: /Users/meirgabay/python-project/meirg-ascii.txt Insert your name: willy wonka Hello Willy Wonka, here's the cat fact of the day: Siamese kittens are born white because of the heat inside the mother's uterus before birth. This heat keeps the kittens' hair from darkening on the points. 

Executing the module src/appy/utils/message.py from the root dir

# Doesn't contain relative imports # Executing as a script - no errors since there are no relative imports (python-project) $ python src/appy/utils/message.py My Path: python-project/src/appy/utils/message.py # Executing as a module - works as expected (python-project) $ python -m src.appy.utils.message python-project/src/appy/utils/message.py 

If the PWD is a subdirectory of the project, such as python-project/src/appy , an attempt to execute a module which contains relative imports, will raise the exception below. Remember, your PWD should always be the project’s root directory, in this case, it’s python-project .

# PWD is `src/appy` # Execute as a module - issues when running from a subdirectory (not from root dir) (python-project/src/appy) $ python -m core.app Traceback (most recent call last): File "/Users/meirgabay/.pyenv/versions/3.8.2/Python.framework/Versions/3.8/lib/python3.8/runpy.py", line 193, in _run_module_as_main return _run_code(code, main_globals, None, File "/Users/meirgabay/.pyenv/versions/3.8.2/Python.framework/Versions/3.8/lib/python3.8/runpy.py", line 86, in _run_code exec(code, run_globals) File "/Users/meirgabay/python-project/src/appy/core/app.py", line 1, in from ..utils import message, img_ascii ValueError: attempted relative import beyond top-level package 

It doesn’t happen when invoking message , since message doesn’t use relative imports

# Execute as a script - works because there are no relative imports to parent packages, similar to main.py (python-project/src/appy) $ python utils/message.py My Path: python-project/src/appy/utils/message.py # Execute as a module - works as expected, no imports of parent packages (python-project/src/appy) $ python -m utils.message My Path: python-project/src/appy/utils/message.py 

Invoke a function from the command-line

Trying to invoke a function from the terminal, such as appy.core.app.main() , will raise the ModuleNotFound exception. A package must be imported before invoking one of its functions.

# Execute as a module - must import the function before invoking it (python-project) $ python -m src.appy.core.app.main /Users/meirgabay/.pyenv/versions/3.8.2/Python.framework/Versions/3.8/bin/python: Error while finding module specification for 'src.appy.core.app.main' (ModuleNotFoundError: __path__ attribute not found on 'src.appy.core.app' while trying to find 'src.appy.core.app.main') 

Since you can’t invoke main() directly from the terminal, calling it from the if __main__ block enables executing it from the terminal. It’s possible to pass arguments, but it’s a bit ugly, read the docs to learn how. The following example attempts to execute the module appy.core.app , which in turn call its if __main__ block

# Execute as a module - works due to the `if __main__` block (python-project) $ python -m src.appy.core.app My Path: python-project/src/appy/core/app.py Created the file: /Users/meirgabay/python-project/meirg-ascii.txt Insert your name: willy wonka Hello Willy Wonka, here's the cat fact of the day: Cats sleep 16 to 18 hours per day. When cats are asleep, they are still alert to incoming stimuli. If you poke the tail of a sleeping cat, it will respond accordingly. 

Invoking a function from the terminal is also possible by using the -c flag. Surprise, it’s possible to pass arguments in a more intuitive way, for example src.app.main(my_arg1, my_arg2)

# Execute inline script - providing the "-c" flag with the command as a string, the semi-colon ";" means break-row (python-project) $ python -c "import src.appy.core.app as app; app.main()" Created the file: /Users/meirgabay/python-project/meirg-ascii.txt Insert your name: willy wonka Hello Willy Wonka, here's the cat fact of the day: Cats can be right-pawed or left-pawed. 

What are the available command-line flags in Python?

• In this tutorial, we used both -c and -m flags
• Read the docs to learn about more flags — Using cmdline

Why is it possible to execute python -m src.appy ?

The src/appy/__main__.py file acts like the if __main__ code snippet, but on packages. This enables the appy package to be executed with python -m or with runpy

# Execute as a module (python-project) $ python -m src.appy My Path: python-project/src/appy/__main__.py Created the file: /Users/meirgabay/python-project/meirg-ascii.txt Insert your name: willy wonka Hello Willy Wonka, here's the cat fact of the day: One reason that kittens sleep so much is because a growth hormone is released only during sleep. 

What’s runpy and why do you use it in main.py ?

The runpy package provides the ability to run modules from a module (Python script). This package is shipped with Python so there’s no need to install it.

import runpy def main(): appy_package = runpy.run_module( mod_name="src.appy", init_globals=globals()) appy_package['message'].script_path(__file__) appy_package['main']() if __name__ == "__main__": main() 

What’s globals() ?

The official definition from the docs

Return a dictionary representing the current global symbol table. This is always the dictionary of the current module (inside a function or method, this is the module where it is defined, not the module from which it is called).

(python-project) $ python Python 3.8.2 (default, Jun 30 2020, 19:04:41) [Clang 11.0.3 (clang-1103.0.32.59)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> globals() '__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': '_frozen_importlib.BuiltinImporter'>, '__spec__': None, '__annotations__': <>, '__builtins__': 'builtins' (built-in)>> 

This blog post is part of the Python Project series, and is based on this GitHub repository — unfor19/python-project.
The GitHub repo includes an example of a Python project, and Wiki Pages that describe the necessary steps for developing, creating and distributing a Python package.

Originally published at github.com/unfor19/python-project on 3 November, 2020

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Get Process By Name in Python

You can get a process by name by searching through all active child processes for a process with a given name.

In this tutorial you will discover how to get a process by name in Python.

Need To Get a Process By Name

A process is a running instance of a computer program.

Every Python program is executed in a Process, which is a new instance of the Python interpreter. This process has the name MainProcess and has one thread used to execute the program instructions called the MainThread. Both processes and threads are created and managed by the underlying operating system.

Sometimes we may need to create new child processes in our program in order to execute code concurrently.

Python provides the ability to create and manage new processes via the multiprocessing.Process class.

You can learn more about multiprocessing in the tutorial:

In multiprocessing, we may need to get a process by name.

This may be for many reasons, such as:

• We don’t have the pid of the process.
• Report details of the process.
• Send a signal to the process, like SIGKILL to kill it.

How can we get a process by name?

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How to Get a Process By Name

The Python standard library does not provide a mechanism to search through processes by name.

Instead, we can develop this functionality ourselves.

In this section we will explore how we might search for a process by its name.

Process Names

Python processes have names.

They are accessible via the name attribute on the multiprocessing.Process class instance for the process.

Process names are not unique.

The default names assigned to processes attempt to be unique, e.g. Process-1, Process-2, and so on. The name of processes can be changed at any time by the process itself or another process.

You can learn more about process names in the tutorial:

As such, we cannot rely on the name of a process being unique generally.

Nevertheless, within our application, we may assign distinct and meaningful names to processes. These names could then be used uniquely.

List Processes

In order to get a process by name, we need to be able to get a list of all processes, then search through them.

Within Python, we cannot get a list of all processes directly.

Instead, we can get a list of all active child processes for the current parent process.

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