BUG: Index.is_monotonic... incorrectly caching Index.is_unique when first value is NaT by lukemanley · Pull Request #55755 · pandas-dev/pandas (original) (raw)

In [1]: import pandas as pd

In [2]: idx = pd.to_datetime([None, "2000-01-01", "2000-01-01"])

In [3]: idx.is_unique, idx.is_monotonic_increasing
Out[3]: (False, False)

In [4]: idx = pd.to_datetime([None, "2000-01-01", "2000-01-01"])

In [5]: idx.is_monotonic_increasing, idx.is_unique
Out[5]: (False, True)