PySwissEphe - Swiss Ephemeris

2.10.3.2 · active · verified Mon Apr 13

PySwissEphe is a Python extension providing access to the powerful Swiss Ephemeris library, a high-precision astronomical calculation engine. It allows for calculation of planetary positions, houses, aspects, and other celestial data. Currently at version 2.10.3.2, the library maintains a steady release cadence, often updating to reflect new versions of the underlying Swiss Ephemeris C code.

Warnings

gotcha The `swe.swe_set_ephe_path()` function must be called with a valid path to the Swiss Ephemeris data files (.se1). Without these files, calculations will fail, often with cryptic error messages or silently incorrect results.
Fix: Download the necessary ephemeris data files from the official Swiss Ephemeris website (www.astro.com/swisseph/sweph_e.htm) and ensure the provided path is correct.
gotcha The library exposes numerous constants (e.g., `swe.SE_JUL_CAL`, `swe.SE_SUN`, `swe.SEFLG_SWIEPH`) that control calculation parameters and celestial bodies. Misunderstanding or incorrect use of these constants can lead to inaccurate astronomical calculations without explicit Python errors.
Fix: Refer to the official Swiss Ephemeris documentation and `pyswisseph` examples to understand the purpose and correct usage of these constants for your specific astrological or astronomical needs.
breaking As a wrapper for the Swiss Ephemeris C library, `pyswisseph` versions directly correspond to the upstream library's version. Updates to the C library can introduce breaking changes, bug fixes, or new features that subtly affect calculation precision or behavior, especially in edge cases.
Fix: Always consult the release notes for both `pyswisseph` and the underlying Swiss Ephemeris C library when upgrading, and validate critical calculations after an update.

Install

pip install pyswisseph Install latest version

Imports

swisseph
```
import swisseph as swe
```
The convention is to import swisseph and alias it as swe for brevity and consistency with the original Swiss Ephemeris API.

Quickstart

This quickstart demonstrates how to initialize PySwissEphe, set the ephemeris data path, and calculate a planet's position. Note that accurate calculations require downloading Swiss Ephemeris data files (.se1) and placing them in the specified `ephe_dir`.

import swisseph as swe
import os

# IMPORTANT: For accurate calculations, you need to download the Swiss Ephemeris
# data files (e.g., 'se1900-2050.se1', 'seasr.se1') from the official website
# (www.astro.com/swisseph/sweph_e.htm) and place them in a directory.
# For this example, we create an empty 'swefiles' directory in the current
# working directory. Calculations will fail or return errors without the actual files.

ephe_dir = 'swefiles'
if not os.path.exists(ephe_dir):
    os.makedirs(ephe_dir)
    print(f"Created directory '{ephe_dir}'. Please populate it with Swiss Ephemeris data files.")

# Set the path to the ephemeris data files
swe.swe_set_ephe_path(ephe_dir)

# Define a Julian Day (UT - Universal Time) for calculation
# January 1, 2024, 12:00 UT
jd_ut = swe.swe_julday(2024, 1, 1, 12.0, swe.SE_GREG_CAL)

# Define calculation flags: use default Swiss Ephemeris, calculate speed
flags = swe.SEFLG_SWIEPH | swe.SEFLG_SPEED

# Calculate Mars' position (SE_MARS)
# xx will contain: [longitude, latitude, distance, speed_longitude, speed_latitude, speed_distance]
xx, ret = swe.swe_calc_ut(jd_ut, swe.SE_MARS, flags)

if ret >= 0:
    print(f"Mars' position on 2024-01-01 12:00 UT:")
    print(f"  Longitude: {xx[0]:.4f}°")
    print(f"  Latitude:  {xx[1]:.4f}°")
    print(f"  Distance:  {xx[2]:.4f} AU")
    print(f"  Speed Longitude: {xx[3]:.4f}°/day")
else:
    print(f"Error calculating Mars' position. Make sure '{ephe_dir}' contains required '.se1' files.")
    print(f"Swiss Ephemeris error: {swe.swe_get_serr_string(ret)}")

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