Musterlsg dict list | Python Fiddle

courses = {
  'mar2014': ( 	
            {
                   'lecture_id'	: 'P1',
                   'name'   : 'Programmierung I',
                   'author' : 'N.N.',
                   'teacher': 'Loose'
                   },
			{
                   'lecture_id'	: 'P2',
                   'name'   : 'Programmierung II',
                   'teacher': 'Loose',
                   'author' : 'N.N.',
                   'prereq' : 'P1'
                   },
			{
                   'lecture_id'	: 'DB',
                   'name'   : 'Datenbanken',
                   'teacher': 'Preuss',
                   'author' : 'Li'
                   }
           	),
  'sep2014': (
              {
                      'lecture_id'	: 'OOSL',
                      'name'   : 'OO Skriptsprachen',
                      'teacher': 'Preuss'
                      },
              {
	                  'lecture_id'	: 'DB',
                      'name'   : 'Datenbanken',
                      'teacher': 'Preuss',
                      'author':  'Li'
                      }
              ),
  'mar2015': (
              {       'lecture_id'	: 'NoSQL',
				      'name'   : 'NoSQL Datenbanken',
                      'teacher': 'Edlich'
                       },
              )    
}

def is_offered(courses, lecture_id, semester):
    semester_offers = courses.get(semester, None)
    if not semester_offers:
    	return False
    for offer in semester_offers:
        if offer.get('lecture_id', None) == lecture_id:
            return True
    return False

print(is_offered(courses, 'NoSQL', 'mar2015'))
print(is_offered(courses, 'NoSQL', 'sep2014'))
print(is_offered(courses, 'P1', 'mar2015'))

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