How to apply function for only special cells in column pandas?

I have a issue with applying function for column in pandas, please see below code :

import pandas as pd

#create a dict as below
data_dic = {
    "text": ['hello',1,'how are you?',4],
    "odd": [0,2,4,6],
    "even": [1,3,5,7]
}
#create a DataFrame
df = pd.DataFrame(data_dic)
#define function
def checktext(str1):
    if isinstance(str1,str):
        return str1.upper()
def checknum(str1):
    if isinstance(str1,int):
        return str1+1

df['new'] = df['text'].apply(lambda x: checktext(x))
df['new'].head()

my df now show like below:

    text           odd       even   new
0   hello          0          1     HELLO
1   1              2          3     None
2   how are you?   4          5     HOW ARE YOU?
3   4              6          7     None

I would like to apply function checknum for 2 cell in column ‘new’ which is having ‘None’ value. Can someone assist this ? Thank you

Answer

IIUC, you can use vectorial code:

# make string UPPER
s = df['text'].str.upper()
            # where there was no string, get number + 1 instead
df['new'] = s.fillna(df['text'].where(s.isna())+1)

output:

           text  odd  even           new
0         hello    0     1         HELLO
1             1    2     3             2
2  how are you?    4     5  HOW ARE YOU?
3             4    6     7             5

That said, for the sake of the argument, your 2 functions could be combined into one:

def check(str1):
    if isinstance(str1,str):
        return str1.upper()
    elif isinstance(str1,int):
        return str1+1

df['new'] = df['text'].apply(check)