Using Names

Names is different from the other classes in data in that it does not use DataClass as a base class. Instead, Names does not contain any data, it merely serves as an umbrella for functions to identify asteroid and comet names, numbers, and designations.

In order to distinguish if a string designates a comet or an asteroid, you can use the following code:

>>> from sbpy.data import Names
>>> Names.asteroid_or_comet('(1) Ceres')
'asteroid'
>>> Names.asteroid_or_comet('2P/Encke')
'comet'

The module basically uses regular expressions to match the input strings and find patterns that agree with asteroid and comet names, numbers, and designations. There are separate tasks to identify asteroid and comet identifiers:

>>> Names.parse_asteroid('(228195) 6675 P-L') # doctest: +SKIP
{'number': 228195, 'desig': '6675 P-L'}
>>> Names.parse_asteroid('C/2001 A2-A (LINEAR)') # doctest: +SKIP
... sbpy.data.names.TargetNameParseError: C/2001 A2-A (LINEAR) does not appear to be an asteroid identifier
>>> Names.parse_comet('12893') # doctest: +SKIP
... sbpy.data.names.TargetNameParseError: 12893 does not appear to be a comet name
>>> Names.parse_comet('73P-C/Schwassmann Wachmann 3 C') # doctest: +SKIP
{'type': 'P', 'number': 73, 'fragment': 'C', 'name': 'Schwassmann Wachmann 3 C'}

In order to be able to distinguish between asteroid and comet identifiers, sbpy follows the MPC guideline in that it requires comet identifiers to include the comet type in either in combination with a number (e.g., '259P'), a name (e.g., 'P/Halley'), or both (e.g., '2P/Encke'). For instance, the identifier 'Halley' would be identified as an asteroid, as it lacks a comet type identifier. Hence, some caution is advised when using these routines - identification might not be unambiguous.

Sorting names with a natural sort order

Sorting with Python’s built-in functions might not return the desired order:

>>> comets = ['9P/Tempel 1',
...           '101P/Chernykh',
...           '10P/Tempel 2',
...           '2P/Encke']
>>> sorted(comets)
['101P/Chernykh', '10P/Tempel 2', '2P/Encke', '9P/Tempel 1']

101P and 10P are placed at the start of the list because Python is performing a string comparison, which is character-by-character, and '1' < '2'. With sbpy’s natural_sort_key, numerical comparisons are made whenever possible:

>>> from sbpy.data import natural_sort_key
>>> sorted(comets, key=natural_sort_key)
['2P/Encke', '9P/Tempel 1', '10P/Tempel 2', '101P/Chernykh']

Packed Numbers and Designations

from_packed and to_packed provide functionality to convert between packed designations and numbers and unpacked ones:

>>> Names.from_packed('J95A01A')
'1995 AA1'
>>> Names.from_packed('G3693')
163693
>>> Names.to_packed('1995 AA1')
'J95A01A'
>>> Names.to_packed('163693')
'G3693'