My while function is not returning any value ! What am i doing wrong

Quite newbie to this !

i have a dataframe that looks like this:

currentMilestone            m2          SLA_M6          latedeliverydate            SLA_M3          earlypickupdate
            m2      2020-02-21      2020-02-18              2020-03-14          2020-02-09              2020-02-08
            m2      2020-02-21      2020-02-18              2020-02-14          2020-02-09              2020-02-08
            m2      2020-02-21      2020-02-18              2020-02-14          2020-02-09              2020-02-08
            m2      2020-02-21      2020-02-18              2020-02-14          2020-02-09              2020-02-08
            m1             NaT      2020-03-24              2020-02-14          2020-03-13              2020-03-18

i have written that looks like this:

def flag(data):

    while data.currentMilestone== 'm1'is True:

        if data.SLA_M6  > data.latedeliverydate:
            return 'R'
        elif (data.SLA_M3 != data.earlypickupdate) & (data.latedeliverydate <= data.SLA_M6):
            return 'A'

        elif (data.SLA_M3 == data.earlypickupdate) & (data.latedeliverydate >= data.earlypickupdate):
            return 'G'
        else:
            return None

the expected output is :

currentMilestone            m2          SLA_M6          latedeliverydate            SLA_M3          earlypickupdate         flag
            m2      2020-02-21      2020-02-18              2020-03-14          2020-02-09              2020-02-08          None    
            m2      2020-02-21      2020-02-18              2020-02-14          2020-02-09              2020-02-08          None
            m2      2020-02-21      2020-02-18              2020-02-14          2020-02-09              2020-02-08          None
            m2      2020-02-21      2020-02-18              2020-02-14          2020-02-09              2020-02-08          None
            m1             NaT      2020-03-24              2020-02-14          2020-03-13              2020-03-18            R

When i run my function i dont have any result … I mean the flag is not working properly. All rows are set to None

What wrong here ?

Answer

Use numpy.select for this since apply is very inefficient:

import numpy as np

cond1 = data['currentMilestone'] == 'm1'

condlist = [
    (data['SLA_M6'] > data['latedeliverydate']) & cond1,
    (data['SLA_M3'] != data['earlypickupdate']) & (data['latedeliverydate'] <= data['SLA_M6']) & cond1,
    (data['SLA_M3'] == data['earlypickupdate']) & (data['latedeliverydate'] >= data['earlypickupdate']) & cond1
]

choicelist = ['R', 'A', 'G']

data['flag'] = np.select(condlist, choicelist, default=None)

[out]

  currentMilestone         m2     SLA_M6 latedeliverydate     SLA_M3 earlypickupdate  flag
0               m2 2020-02-21 2020-02-18       2020-03-14 2020-02-09      2020-02-08  None
1               m2 2020-02-21 2020-02-18       2020-02-14 2020-02-09      2020-02-08  None
2               m2 2020-02-21 2020-02-18       2020-02-14 2020-02-09      2020-02-08  None
3               m2 2020-02-21 2020-02-18       2020-02-14 2020-02-09      2020-02-08  None
4               m1        NaT 2020-03-24       2020-02-14 2020-03-13      2020-03-18     R