Basics of SpiceyPy

Environment Set-up

Follow the installation instructions provided in installation.

Confirm SpiceyPy installation

There are multiple ways to verify your SpiceyPy installation. The first test is to simply run

pip list

You should see SpiceyPy in the list of your installed packages. If SpiceyPy is not present in the list then a configuration issue in your environment caused SpiceyPy to be installed in a non-standard way. Note this is an error prone to systems with multiple installed python versions.

If SpiceyPy is present in the pip list, then SpiceyPy is installed. Another verification step is within the python REPL run:

import spiceypy as spice

The version of the installed cspice toolkit (note: not SpiceyPy’s version) should be printed out. Otherwise the Python interpreter should output an explanitory error message.

A simple example program

The following calls the SPICE function spiceypy.spiceypy.tkvrsn() which outputs the version of cspice that SpiceyPy is wrapping.

import spiceypy as spice


This should output the following string:



SpiceyPy by default checks the spice error system for errors after all function calls and will raise SpiceyErrors (a python exception) when spice indicates an error. The exception message is a string that follows the format used elsewhere in spice and includes the toolkit version, the short description, explanation, long format description, and traceback (of spice calls). Read the NAIF tutorial on exceptions here.

Also, by default SpiceyPy captures the ‘found’ flags some functions return as it is not idiomatic to python and instead through a SpiceyError exception. This can be temporarily disabled using the spiceypy.spiceypy.no_found_check() context manager that allows the found flag to be returned to the user for action. Outside the context SpiceyPy functions will revert to default behavior.

import spiceypy as spice

spice.bodc2n(-9991) # will raise an exception

with spice.no_found_check():
    name, found = spice.bodc2n(-9991) # found is now available, no exception raised!
    assert not found # found is going to be False in this case.

spice.bodc2n(-9991) # will raise an exception again

There is also an accompanying context manager for enabling the default spiceypy behavior within a code block like so:

import spiceypy as spice

spice.bodc2n(-9991) # will raise an exception

with spice.found_check():
    name = spice.bodc2n(-9991) # will also raise an exception

In addition, for advanced users there are two function spiceypy.spiceypy.found_check_off() and spiceypy.spiceypy.found_check_on() which will disable and enable the behavior without use of the context manager. Additionally, a method spiceypy.spiceypy.get_found_catch_state() allows users to query the current state of found flag catching setting.