Infrastructure for reporting configuration errors via exceptions

Once the actual config-parsing code start raising these exceptions
instead of directly calling sys.exit(), the user experience would
deteriorate due to raw exception traces. There's little value in the
trace itself, so just wrap the whole config loading with pretty error
formatting.

We still do not point to a specific place where that error is defined
(such as a line/column in a given JSON file) because that information is
already lost by the time we perform these checks.

Also, these checks are largely open-coded ad-hoc stuff. Some required
items are not covered, raising KeyError instead. We should get a formal
schema for these...

examples/path_requests_run.py

@@ -30,6 +30,7 @@ from gnpy.core.utils import db2lin, lin2db
 from gnpy.core.request import (Path_request, Result_element, compute_constrained_path,
                               propagate, jsontocsv, Disjunction, compute_path_dsjctn, requests_aggregation,
                               propagate_and_optimize_mode)
+from gnpy.core.exceptions import ConfigurationError
 from copy import copy, deepcopy
 from textwrap import dedent
 from math import ceil
@@ -306,15 +307,19 @@ if __name__ == '__main__':
     print('\x1b[1;34;40m'+f'Computing path requests {args.service_filename} into JSON format'+ '\x1b[0m')
     # for debug
     # print( args.eqpt_filename)
-    data = load_requests(args.service_filename,args.eqpt_filename)
-    equipment = load_equipment(args.eqpt_filename)
-    network = load_network(args.network_filename,equipment)
+    try:
+        data = load_requests(args.service_filename,args.eqpt_filename)
+        equipment = load_equipment(args.eqpt_filename)
+        network = load_network(args.network_filename,equipment)
+    except ConfigurationError as e:
+        print('\x1b[1;31;40m' + 'Configuration error:' + '\x1b[0m' + f' {e}')
+        exit(1)
 
     # Build the network once using the default power defined in SI in eqpt config
     # TODO power density : db2linp(ower_dbm": 0)/power_dbm": 0 * nb channels as defined by
-    # spacing, f_min and f_max 
+    # spacing, f_min and f_max
     p_db = equipment['SI']['default'].power_dbm
-    
+
     p_total_db = p_db + lin2db(automatic_nch(equipment['SI']['default'].f_min,\
         equipment['SI']['default'].f_max, equipment['SI']['default'].spacing))
     build_network(network, equipment, p_db, p_total_db)
@@ -322,7 +327,7 @@ if __name__ == '__main__':
 
     rqs = requests_from_json(data, equipment)
 
-    # check that request ids are unique. Non unique ids, may 
+    # check that request ids are unique. Non unique ids, may
     # mess the computation : better to stop the computation
     all_ids = [r.request_id for r in rqs]
     if len(all_ids) != len(set(all_ids)):
@@ -341,7 +346,7 @@ if __name__ == '__main__':
     # need to warn or correct in case of wrong disjunction form
     # disjunction must not be repeated with same or different ids
     dsjn = correct_disjn(dsjn)
-        
+
     # Aggregate demands with same exact constraints
     print('\x1b[1;34;40m'+f'Aggregating similar requests'+ '\x1b[0m')
 
@@ -350,7 +355,7 @@ if __name__ == '__main__':
 
     print('\x1b[1;34;40m'+'The following services have been requested:'+ '\x1b[0m')
     print(rqs)
-    
+
     print('\x1b[1;34;40m'+f'Computing all paths with constraints'+ '\x1b[0m')
     pths = compute_path_dsjctn(network, equipment, rqs, dsjn)
 
@@ -360,7 +365,7 @@ if __name__ == '__main__':
     end = time.time()
     print(f'computation time {end-start}')
     print('\x1b[1;34;40m'+f'Result summary'+ '\x1b[0m')
-    
+
     header = ['req id', '  demand','  snr@bandwidth','  snr@0.1nm','  Receiver minOSNR', '  mode', '  Gbit/s' , '  nb of tsp pairs']
     data = []
     data.append(header)
@@ -377,7 +382,7 @@ if __name__ == '__main__':
     firstcol_width = max(len(row[0]) for row in data )   # padding
     secondcol_width = max(len(row[1]) for row in data )   # padding
     for row in data:
-        firstcol = ''.join(row[0].ljust(firstcol_width)) 
+        firstcol = ''.join(row[0].ljust(firstcol_width))
         secondcol = ''.join(row[1].ljust(secondcol_width))
         remainingcols = ''.join(word.center(col_width,' ') for word in row[2:])
         print(f'{firstcol} {secondcol} {remainingcols}')
@@ -396,4 +401,3 @@ if __name__ == '__main__':
             with open(fnamecsv,"w", encoding='utf-8') as fcsv :
                 jsontocsv(temp,equipment,fcsv)
                 print('\x1b[1;34;40m'+f'saving in {args.output} and {fnamecsv}'+ '\x1b[0m')
-