如何更改列表中的元素[重复]

final_structure = [ tuple([ j if isinstance(j, str) else "MissingValue" for j in l ]) for l in list_of_tuples ]

np.nan "MissingValue" isinstance()

import numpy as np

list_of_tuples = [['portugal', np.nan, 'japan'], [np.nan, 'germany', 'canada'], ['UK', 'US', np.nan]]
list_of_tuples = map(lambda x: tuple(["MissingValue" if i is np.nan else i for i in x]), list_of_tuples)
print(list_of_tuples)

[('portugal', 'MissingValue', 'japan'), ('MissingValue', 'germany', 'canada'), ('UK', 'US', 'MissingValue')]