cohort_retention=cohort_result.iloc[:,1:].divide(cohort_sizes,axis=0)

This line of code is calculating the retention rate for each cohort in a cohort analysis.

- `cohort_result` contains the number of customers who made a purchase in each month since they joined the company.
- `.iloc[:,1:]` is selecting all columns except the first one (which contains the cohort size).
- `divide` is dividing each value in the selected columns by the corresponding cohort size. This gives us the retention rate for each month since the customer joined the company, relative to the size of the cohort.
- `cohort_sizes` contains the size of each cohort (i.e. the number of customers who joined in each month).
- `axis=0` specifies that we want to divide each row by the corresponding value in `cohort_sizes`.

The resulting `cohort_retention` dataframe contains the retention rate for each cohort and each month since they joined the company.