Example of handling simple data file with stdlib only

simple.py

@@ -0,0 +1,73 @@
+import sys as trans
+import csv
+import pprint
+
+def main():
+    if len(trans.argv) != 2:
+        print("Requires exactly one argument: the CSV to process.")
+        trans.exit(1)
+
+    filename = trans.argv[1]
+
+    # data we will parse from the CSV
+    # we assume that participant IDs and event names are unique
+    participants = {}
+    events = {}
+
+    # the docs say we must use newline='' if passing in a file-like object
+    with open(filename, newline='') as file:
+        # deduce the format of the CSV file by looking at the first
+        #   kilobyte of data
+        dialect = csv.Sniffer().sniff(file.read(1024))
+        # rewind the file to its start
+        file.seek(0)
+        reader = csv.DictReader(file, dialect=dialect)
+
+        for row in reader:
+            # grap all the data from the row. this makes the code below less
+            # verbose and also ensures all data is present - "fail fast"
+            participant_id = row['Participant ID']
+            participant_name = row['Participant Name']
+            event_name = row['Event Name']
+            event_type = row['Event Type']
+
+            # if this participant has not yet been seen, record them
+            if participant_id not in participants:
+                participants[participant_id] = {
+                    'name': participant_name,
+                    'events': []
+                }
+
+            # if this event has not yet been seen, record it
+            # note that we trust the event type from the first occurrance
+            if event_name not in events:
+                events[event_name] = {
+                    'type': event_type,
+                    'participants': []
+                }
+
+            # record this attendance on both the participant and event
+            participants[participant_id]['events'] += [event_name]
+            events[event_name]['participants'] += [participant_name]
+
+    # print all the data
+    pprint.pp(participants)
+    pprint.pp(events)
+
+    print()
+
+    # print attendee stats
+    for pid in participants.keys():
+        name = participants[pid]['name']
+        num_events = len(participants[pid]['events'])
+        print(f"{name} ({pid}) attended {num_events} events")
+
+    print()
+
+    # print attendance stats
+    for event_name in events.keys():
+        num_participants = len(events[event_name]['participants'])
+        print(f"{event_name} had {num_participants} attendees")
+
+if __name__ == "__main__":
+    main()