Python Invocation

Rule

Always use python3 explicitly instead of python in shell commands and scripts.

Context

When executing Python code from shell commands, scripts, or automated workflows on systems that may not have a python symlink.

Detection

Observable signals that you need python3:

• Error: bash: python: command not found
• Python scripts failing with "command not found"
• Running on Ubuntu 20.04+ or Debian 11+ systems
• Working with Docker images or CI/CD pipelines

Pattern

# Wrong: assumes python exists
python script.py  # Error: command not found

# Correct: explicit python3
python3 script.py

# Wrong: shebang assuming python exists
#!/usr/bin/env python

# Correct: explicit python3 shebang
#!/usr/bin/env python3

# Wrong: subprocess with python
import subprocess
subprocess.run(['python', 'script.py'])

# Correct: subprocess with python3
subprocess.run(['python3', 'script.py'])

Outcome

Following this pattern results in:

• System compatibility: Works on Ubuntu 20.04+, Debian 11+, modern Docker images
• Reliability: python3 is guaranteed on Python 3 systems
• Consistency: Same command works across all environments
• PEP 394 compliance: Follows Python's official recommendation

Benefits:

• Prevents "command not found" errors
• Works on systems without python symlink
• Explicit about Python version used
• Compatible with CI/CD workflows

Related

• Python File Execution - Context-aware execution methods
• Shell Command Chaining - Combining commands
• PEP 394 - Python version specification