Add a function for reading an ASCII header file

Fixes #9.

jplephem/ascii.py

@@ -0,0 +1,57 @@
+"""Support function for parsing JPL ephemeris text files.
+
+This is for parsing a NASA ephemeris text header file, like:
+
+ftp://ssd.jpl.nasa.gov/pub/eph/planets/ascii/de421/header.421
+
+You can use this routine like this::
+
+    from jplephem.ascii import parse_header
+    d = parse_header(open('header.421'))
+
+    from pprint import pprint
+    pprint(d)
+    pprint(dict(zip(d['names'], d['values'])))
+
+"""
+import numpy as np
+
+
+def parse_header(lines):
+    lines = iter(lines)
+
+    while next(lines).strip() != 'GROUP   1030':
+        continue
+    assert next(lines).strip() == ''
+    jalpha, jomega, jdelta = (float(s) for s in e(next(lines)).split())
+
+    while next(lines).strip() != 'GROUP   1040':
+        continue
+    assert next(lines).strip() == ''
+    nconstants = int(next(lines))
+    names = []
+    while len(names) < nconstants:
+        names.extend(next(lines).split())
+
+    while next(lines).strip() != 'GROUP   1041':
+        continue
+    assert next(lines).strip() == ''
+    assert int(next(lines)) == nconstants
+    values = []
+    while len(values) < nconstants:
+        values.extend(float(s) for s in e(next(lines)).split())
+
+    while next(lines).strip() != 'GROUP   1050':
+        continue
+    assert next(lines).strip() == ''
+    planet_offsets = np.array(next(lines).split(), np.int_)
+    num_coefficients = np.array(next(lines).split(), np.int_)
+    coefficient_sets = np.array(next(lines).split(), np.int_)
+
+    del lines
+    return(locals())
+
+
+def e(s):
+    """Convert a string in 0.1D+01 FORTRAN notation into 0.1e+10."""
+    return s.replace('D', 'e')