您可以使用itertools.zip_longest: d = [ { "DeltaG": -14.36, "BasePairs": 8, "Dimer": "5' TCAGATGTGTATAAGAGACAGGTGTAATCGTTCCGCTTGAATGTGANGCAAGAA\n : |||||||| : \n3' TAGTCACCTGCGTTCCTGACACTAGCGAGACAGAGAATATGTGTAGAGGCGAGCTAAGGTACTTGAAAGGGTGTATTAGAG", }]from itertools import zip_longest# control print:print(d[0]["Dimer"])print()print("-" * 80)print()for l1, l2, l3 in zip_longest(*d[0]["Dimer"].split("\n")): if l1 == "N" and l2 == "|" and l3 in "TCGA": print('Character | under the "N": ', l1, l3) breakelse: print('No character | under the "N"') Prints: 5' TCAGATGTGTATAAGAGACAGGTGTAATCGTTCCGCTTGAATGTGANGC