Equivalent of R's ifelse in Python

I am ne w to Python so forgive me if this is a basic question. I am in the process of converting my R code into Python. I try to create new variable using data from other two variables. In R I would do the following:

df$new_col <- ifelse(is.na(df$col1) & is.na(df$col2), 99,
                ifelse(is.na(df$col1) & !is.na(df$col2), df$col2,
                      ifelse(is.na(df$col2) & !is.na(df$col1), df$col1,
                            ifelse(df$col2 > df$col1, df$col1,
                                  ifelse(df$col2 < df$col1, df$col2,
                                        ifelse(df$col1==df$col2, df$col2, "Error in coding"))))))

I have seen below bit of code in answers to the similar questions which works when I have only one condition but I can't get it work when it is more complex.

df['new_col'] = np.where(df['col1'].isnull() and df['col2'].isnull(), x, y)

Any help would be greatly appreciated.