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Embedded Python Shells

Python (optional)

If the [cmd2.Cmd][] class is instantiated with include_py=True, then the optional py command will be present and run an interactive Python shell:

from cmd2 import Cmd
class App(Cmd):
    def __init__(self):
        Cmd.__init__(self, include_py=True)

The Python shell can run CLI commands from you application using the object named in self.pyscript_name (defaults to app). This wrapper provides access to execute commands in your cmd2 application while maintaining isolation from the full Cmd instance. For example, any application command can be run with app("command ...").

You may optionally enable full access to your application by setting self.self_in_py to True. Enabling this flag adds self to the python session, which is a reference to your cmd2 application. This can be useful for debugging your application.

Any local or global variable created within the Python session will not persist in the CLI's environment.

Anything in self.py_locals is always available in the Python environment.

All of these parameters are also available to Python scripts which run in your application via the run_pyscript command:

  • supports tab completion of file system paths
  • has the ability to pass command-line arguments to the scripts invoked

This command provides a more complex and powerful scripting capability than that provided by the simple text file scripts. Python scripts can include conditional control flow logic. See python_scripting.py cmd2 and the conditional.py script for an example of how to achieve this in your own applications. See Scripting for an explanation of both scripting methods in cmd2 applications.

A simple example of using run_pyscript is shown below along with the arg_printer script:

(Cmd) run_pyscript examples/scripts/arg_printer.py foo bar baz
Running Python script 'arg_printer.py' which was called with 3 arguments
arg 1: 'foo'
arg 2: 'bar'
arg 3: 'baz'

IPython (optional)

If IPython is installed on the system and the cmd2.Cmd class is instantiated with include_ipy=True, then the optional ipy command will run an interactive IPython shell:

from cmd2 import Cmd
class App(Cmd):
    def __init__(self):
        Cmd.__init__(self, include_ipy=True)

The ipy command enters an interactive IPython session. Similar to an interactive Python session, this shell can access your application instance via self if self.self_in_py is True and any changes to your application made via self will persist. However, any local or global variable created within the ipy shell will not persist in the CLI's environment

Also, as in the interactive Python session, the ipy shell has access to the contents of self.py_locals and can call back into the application using the app object (or your custom name).

IPython provides many advantages, including:

  • Comprehensive object introspection
  • Get help on objects with ?
  • Extensible tab completion, with support by default for completion of python variables and keywords
  • Good built-in ipdb debugger

The object introspection and tab completion make IPython particularly efficient for debugging as well as for interactive experimentation and data analysis.
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