Support satellite lookup by integer ID

Fixes #167. Thanks for the good idea, @Tarlan0001!

CHANGELOG.rst

@@ -3,6 +3,13 @@ Changelog
 
 .. currentmodule:: skyfield.positionlib
 
+1.4 — 2018 ?
+------------
+
+* The dictionary of satellites returned when you read a TLE file
+  now supports lookup by integer satellite ID, not just by name.
+  `#167 <https://github.com/skyfielders/python-skyfield/issues/167>`_
+
 1.3 — 2018 April 15
 -------------------
 

skyfield/iokit.py

@@ -354,6 +354,7 @@ def parse_celestrak_tle(fileobj):
         line1 = next(lines).decode('ascii')
         line2 = next(lines).decode('ascii')
         sat = EarthSatellite(line1, line2, name)
+        yield sat.model.satnum, sat
         yield name, sat
         if ' (' in name:
             # Given `ISS (ZARYA)` or `HTV-6 (KOUNOTORI 6)`, also support

skyfield/tests/test_io_parsing.py

@@ -15,6 +15,7 @@
 def test_celestrak():
     f = BytesIO(sample_celestrak_text)
     d = dict(parse_celestrak_tle(f))
-    assert len(d) == 4
-    assert d['ISS'] == d['ISS (ZARYA)'] == d['ZARYA']
-    assert d['FLOCK 2E-1']
+    assert len(d) == 6
+    assert d[25544] is d['ISS'] is d['ISS (ZARYA)'] is d['ZARYA']
+    assert d[41483] is d['FLOCK 2E-1']
+    assert d[25544] is not d[41483]