KnowCardPython · OS, sys, argparse & subprocess
When is running subprocess.run(cmd, shell=True) dangerous, and what's the safer default?
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More in OS, sys, argparse & subprocess
You run an external tool with subprocess.run(["mytool", "--check"]). It fails (exit code 1) but your Python script keeps going as if nothing happened. How do you make the failure raise?
What does `r.stdout` hold after this, and why is `text=True` important?
```
r = subprocess.run(
["echo", "hi"],
capture_output=True, text=True)
```
What are sys.stdin, sys.stdout, and sys.stderr, and why send error/diagnostic messages to stderr rather than stdout?
You read a config value with os.environ["API_KEY"]. It works on your machine but crashes with KeyError on a fresh deploy where the var isn't set. What's the safe way to read it?
What does this print when run as `python prog.py hello`?
```
import sys
print(len(sys.argv))
print(sys.argv[0])
```
A script is called `python add.py 2 3` with this body. What does it print?
```
import sys
print(sys.argv[1] + sys.argv[2])
```
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