Coding Mechanics

[321brian]

I have the following code snippet below:

import pandas as pd
import statsmodels.formula.api as sms

fat = pd.read_csv('https://s3-us-west-2.amazonaws.com/static-resources.zybooks.com/fat.csv')

# Response variable
Y = fat['body_fat_percent']

# Generates the linear regression model
# Multiple predictor variables are joined with +
model = sms.ols('Y ~ triceps_skinfold_thickness_mm + midarm_circumference_cm + thigh_circumference_cm', data = fat).fit()

# Prints a list of the fitted values for each sample
print(model.fittedvalues)

What I want to know is how Python knows to map the variable Y, which is set to a column in a dataframe in line 7, to the "Y" reference in the string in the ols method call on line 11. As far as I can tell, I am just setting Y and then doing nothing with it, but somehow Python knows to reference it in the method call.