import re
text = 'The territory of modern Hungary was for centuries inhabited by a succession of peoples, including Celts, Romans, Germanic tribes, Huns, West Slavs and the Avars. The foundations of the Hungarian state was established in the late ninth century AD by the Hungarian grand prince Árpád following the conquest of the Carpathian Basin. According to previous census City: Budapest (population was: 1,590,316)Debrecen (population was: 115,399)Szeged (population was: 104,867)Miskolc (population was: 109,841). However etc etc'
#p = re.compile(r'City:\s*(.*?)However')
p2 = re.compile(r'(?P<city>\w+)\s*\([^()\d]*(?P<population>\d[\d,]*)')
#m = p.search(text)
#if m:
print([x.groupdict() for x in p2.finditer(text)])

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