import re
out = """{
'cell_type': 'code',
'execution_count': 50,
'metadata': {},
'outputs': [],
'source': 'day = \'2018-03-23\''
}"""
range_day = re.findall(r'day\s*=\s* \'\d*[-,]?\d*[-,]?\d*\'', out)[0].replace(' ', '').replace("'", "")
print(range_day)
aW1wb3J0IHJlCgpvdXQgPSAiIiJ7CiAgICAgICAgJ2NlbGxfdHlwZSc6ICdjb2RlJywKICAgICAgICAnZXhlY3V0aW9uX2NvdW50JzogNTAsCiAgICAgICAgJ21ldGFkYXRhJzoge30sCiAgICAgICAgJ291dHB1dHMnOiBbXSwKICAgICAgICAnc291cmNlJzogJ2RheSA9IFwnMjAxOC0wMy0yM1wnJwp9IiIiCgpyYW5nZV9kYXkgPSByZS5maW5kYWxsKHInZGF5XHMqPVxzKiBcJ1xkKlstLF0/XGQqWy0sXT9cZCpcJycsIG91dClbMF0ucmVwbGFjZSgnICcsICcnKS5yZXBsYWNlKCInIiwgIiIpCgpwcmludChyYW5nZV9kYXkp