Use argparse

Preparing to introduce an option.

cost_function.py

@@ -27,8 +27,8 @@ import datetime
 from numpy import loadtxt
 import report_graph
 import util_eddies
-import sys
 import bisect
+import argparse
 
 def calculate_radii_rossby(start, end, inc, segment, e_overestim, handlers,
                            array_d_init):
@@ -76,9 +76,9 @@ def get_SHPC(array_d_ini, date_index):
 
 t0 = time.perf_counter()
 timings = open("timings.txt", "w")
-
-if len(sys.argv) == 1:
-    sys.exit("Required arguments: SHPC-directory [SHPC-directory] ...")
+parser = argparse.ArgumentParser()
+parser.add_argument("SHPC_dir", nargs='+')
+args = parser.parse_args()
 
 # Grab e_overestim:
 with open("node_id_param.json") as f: node_id_param = json.load(f)
@@ -125,7 +125,7 @@ g.ep['cost_function'] = g.new_ep('float')
 
 # Set up the list of SHPC:
 
-handlers = [util_eddies.open_shpc(shpc_dir) for shpc_dir in sys.argv[1:]]
+handlers = [util_eddies.open_shpc(shpc_dir) for shpc_dir in args.SHPC_dir]
 
 array_d_init = [handler["d_init"] for handler in handlers]
 # (create the list once and for all)