Automation and Scripting / Phase 6: Task Scheduling & Deployment

Running Scripts from the Command Line

Run Python automation scripts reliably from the shell, using venvs and predictable working directories.

1 min readupdated 6 Oct 2026

diagram python script.py and python -m are not the same command mermaid

  flowchart TD
  A["python pkg/mod.py"] --> B["sys.path[0] = pkg/"]
  B --> C["'pkg' itself is NOT importable"]
  C --> D["from pkg import mod -> ModuleNotFoundError"]
  E["python -m pkg.mod"] --> F["sys.path[0] = the current directory"]
  F --> G["'pkg' is importable"]
  G --> H["relative and absolute imports both work"]
  I["__name__"] --> J["'__main__' either way -- the guard behaves the same"]

Both run the same file, but they set up the import system differently. Running a path puts that file's own directory first on sys.path; running a module puts the current directory there instead. That single difference decides whether the file can import the package it lives in.

Measured: the same package, two ways of starting it

Same directory, same cwd, one difference:

Command	`sys.path[0]`
`python pkg/mod.py`	`<project>/pkg` — the script's directory
`python -m pkg.mod`	`<project>` — the current directory

And the consequence, with a module that does from pkg import mod:

Command	Result
`python pkg/mod2.py`	`ModuleNotFoundError: No module named 'pkg'`
`python -m pkg.mod2`	works

This is the single most common "but it imports fine in my editor" problem. The file has not changed and neither has the working directory — only the way the interpreter was invoked.

The rule: anything inside a package should be started with -m. A plain python path/to/file.py is for standalone scripts that import nothing local. Adding sys.path.append("..") to work around it appears to fix the symptom and breaks as soon as the script is run from anywhere else.

Basic run

Shell

python my_script.py

Use a virtual environment

isolate dependencies
avoid “works on my machine”

Working directory tip

Many scripts break because they assume the current directory.

Prefer pathlib.Path(__file__):

Python

from pathlib import Path
 
BASE_DIR = Path(__file__).resolve().parent
print(BASE_DIR)

🧪 Try It Yourself

Exercise 1 – List Files with os.listdir

exerciseYour turn

script.py

Output

Press Run to see what your code prints.

Exercise 2 – Join Paths with os.path.join

exerciseYour turn

script.py

Output

Press Run to see what your code prints.

Exercise 3 – Write and Read a File

exerciseYour turn

script.py

Output

Press Run to see what your code prints.

Running Scripts from the Command Line

Basic run

Use a virtual environment

Working directory tip

🧪 Try It Yourself

Exercise 1 – List Files with os.listdir

Exercise 2 – Join Paths with os.path.join

Exercise 3 – Write and Read a File

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