pandas.notnull function

see

https://pandas.pydata.org/pandas-docs/version/0.23.0/generated/pandas.notnull.html#

The source:

https://github.com/pandas-dev/pandas/blob/v0.23.0/pandas/core/dtypes/missing.py#L259-L336

The key point:

notnull = notna

所以notnull这个函数就是notna函数。