na_rep 参数代表什么？

Question

I am looking at cat method in Pandas

I can not grasp what is na_rep .

Answer 1

Docs about Series.str.cat says:

When na_rep is None (default behavior), NaN value(s) in the Series are ignored.

Series(['a','b',np.nan,'c']).str.cat(sep=' ')  
'a b c'

Series(['a','b',np.nan,'c']).str.cat(sep=' ', na_rep='?')  
'a b ? c'