Add README

README.md

+# `asccol` ASCII Columnar Data Parser
+
+Use this simple library to parse aligned text data into Python named
+tuples, using your own specifications for keyword, type, and column
+width.
+
+## Example usage
+
+```py
+import math
+import sys
+from asccol import DataSpec, Columns, parse_data
+
+def simple_time(s):
+    """Convert a HHMM string to an (H, M) tuple."""
+    hour = s[:2]
+    minute = s[2:4]
+    return tuple(map(int, (hour, minute)))
+
+def filtered_float(s):
+    """Like float, but ignore the special value 444.0."""
+    val = float(s)
+    return val if val != 444.0 else math.nan
+
+# 10 minute data
+# See https://amrc.ssec.wisc.edu/data/ftp/pub/aws/q10/q10readme.txt
+Q10 = DataSpec(
+    leading=2,  # lines to delete
+    cols=Columns(
+        ('year', int, 4),  # keyword, type (converter function), width
+        ('jdate', int, 4),
+        ('month', int, 3),
+        ('date', int, 3),
+        ('time', simple_time, 5),
+        ('temp', filtered_float, 7),
+        ('pressure', filtered_float, 7),
+        ('wind_speed', filtered_float, 7),
+        ('wind_dir', filtered_float, 7),
+        ('rel_hum', filtered_float, 7),
+        ('delta_t', filtered_float, 7),
+    ),
+)
+
+for row in parse_data(sys.stdin, Q10):
+    print(row)
+```
+
+The program above will transform this input:
+
+```
+Year: 2021  Month: 02  ID: BYD  ARGOS:  8903  Name: Byrd
+Lat: 80.02S  Lon: 119.44W  Elev: 1539m
+2021  32  2  1 0000  -16.3  803.9    8.9   22.0   79.0  444.0
+2021  32  2  1 0010  -16.4  803.9    8.6   25.0   79.0  444.0
+```
+
+...into this output:
+
+```
+row(year=2021, jdate=32, month=2, date=1, time=(0, 0), temp=-16.3, pressure=803.9, wind_speed=8.9, wind_dir=22.0, rel_hum=79.0, delta_t=nan)
+row(year=2021, jdate=32, month=2, date=1, time=(0, 10), temp=-16.4, pressure=803.9, wind_speed=8.6, wind_dir=25.0, rel_hum=79.0, delta_t=nan)
+```