Final answer:
To check for an installed Python package, use the pip command 'pip show package_name' in the command-line, or try to import the package in a Python script and catch a ModuleNotFoundError.
Step-by-step explanation:
To check if a Python package is installed, one can use the command-line interface with the pip tool (which is the Python package installer) by typing pip show package_name, where package_name is the name of the package you want to check. To check for an installed Python package, use the pip command 'pip show package_name' in the command-line, or try to import the package in a Python script and catch a ModuleNotFoundError.
If the package is installed, pip will show information about it, including the version number. Alternatively, within a Python script or a Python interactive shell, you can use the import statement with a try-except block to attempt to import the package. If the package is not found, a ModuleNotFoundError will be raised.