Properly Using PyMeeus¶
It is very common to try to run PyMeeus like this:
import pymeeus
mydate = pymeeus.Epoch(1992, 10, 13.0)
But if you do that, you’ll get an error like this:
Traceback (most recent call last):
File "/home/user/test/test.py", line 3, in <module>
epoch = pymeeus.Epoch(1992, 10, 13.0)
AttributeError: module 'pymeeus' has no attribute 'Epoch'
This issue points to a misunderstanding that is very common in the
Python world. The keyword import
is used to import MODULES…
but PyMeeus is NOT a module: It is a LIBRARY composed of
MULTIPLE modules (Angle
, Epoch
, Coordinates
, etc). As of
today, the library Pymeeus has 19 different modules (if you look into
the directory where pip
stores the library, you’ll find one “.py”
file per module).
Therefore if you want to use, for example, the module Angle
you
should use:
import pymeeus.Angle
I.e., your module is pymeeus.Angle
, and not just Angle
.
But there is more! When you use import
to fetch a module, you must
then use the dot notation to access the components of the module
(classes, functions, etc). For instance:
import pymeeus.Angle
i = pymeeus.Angle.Angle(11.94524)
In this case, you are telling the Python interpreter that you want to
use the class Angle
(with parameter ‘11.94524’) from the module
Angle
belonging to the library pymeeus
.
There is, however, a more practical (and common) way to handle modules
using the statement from <MODULE> import <COMPONENT>
. For instance:
from pymeeus.Angle import Angle
from pymeeus.Epoch import Epoch, JDE2000
from math import sin, cos, tan, acos, atan2, sqrt, radians, log10
This way is preferred because, among other reasons, only the required components are loaded into memory instead of the whole module. Also, now the component is directly added to your execution environment, which means that you no longer need to use the dot notation.
Therefore, the script at the beginning would become:
from pymeeus.Epoch import Epoch
mydate = Epoch(1992, 10, 13.0)