Fixed name collision.

cohorts.py

@@ -41,10 +41,10 @@ if __name__ == '__main__':
     ada = Patient('Ada', 'UK', 203)
     charles = Patient('Charles', 'UK', 227)
     grace = Patient('Grace', 'US', 112)
-    patients = [ada, charles, grace]
+    all_patients = [ada, charles, grace]
     uk_cohort: Cohort = RegionalCohort('UK')
     young_cohort: Cohort = AgeCohort(0, 225)
     print(f'Charles is in the UK region: {uk_cohort.includes(charles)}')
     print(f'Charles is in the "young" age group: {young_cohort.includes(charles)}')
-    print(f'Everyone in the UK region: {uk_cohort.filter(patients)}')
-    print(f'Everyone in the "young" age group: {young_cohort.filter(patients)}')
+    print(f'Everyone in the UK region: {uk_cohort.filter(all_patients)}')
+    print(f'Everyone in the "young" age group: {young_cohort.filter(all_patients)}')