Using while and if function together with a condition change - python-3.x

Question

I am trying to use python to conduct a calculation which will sum the values in a column only for the time period that a certain condition is met.
However, the summation should begin when the conditions are met (runstat == 0 and oil >1). The summation should then stop at the point when oil == 0.
I am new to python so I am not sure how to do this.
I connected the code to a spreadsheet for testing purposes but the intent is to connect to live data. I figured a while loop in combination with an if function might work but I am not winning.
Basically I want to have the code start when runstat is zero and oil is higher than 0. It should stop summing the values of oil when the oil row becomes zero and then it should write the data to a SQL database (this I will figure out later - for now I just want to see if it can work).
This is what code I have tried so far.
import numpy as np
import pandas as pd
data = pd.read_excel('TagValues.xlsx')
df = pd.DataFrame(data)
df['oiltag'] = df['oiltag'].astype(float)
df['runstattag'] = df['runstattag'].astype(float)
oil = df['oiltag']
runstat = df['runstattag']
def startup(oil,runstat):
while oil.all() > 0:
if oil > 0 and runstat == 0:
totaloil = sum(oil.all())
print(totaloil)
else:
return None
return
print(startup(oil.all(), runstat.all()))
It should sum the values in the column but it is returning: None

Answer 1

OK, so I think that what you want to do is get the subset of rows between the two conditions, then get a sum of those.
Method: Slice the dataframe to get the relevant rows and then sum.
import numpy as np
import pandas as pd
data = pd.read_excel('TagValues.xlsx')
df = pd.DataFrame(data)
df['oiltag'] = df['oiltag'].astype(float)
df['runstattag'] = df['runstattag'].astype(float)
def startup(dframe):
start_row = dframe[(dframe.oiltag > 0) & (dframe.runstattag == 0)].index[0]
end_row = dframe[(dframe.oiltag == 0) & (dframe.index > start_row)].index[0]
subset = dframe[start_row:end_row+1] # +1 because the end slice is non-inclusive
totaloil = subset.oiltag.sum()
return totaloil
print(startup(df))
This code will raise an error if it can't find a subset of rows which match your criteria. If you need to handle that case, then we could add some exception handling.
EDIT: Please note this assumes that your criteria is only expected to occur once per excel. If you have multiple “chunks” that you will want to sum then this will need tweaking.