Load, dedupe, and export
import pandas as pd
customers = pd.read_csv('customers.csv', dtype=str)
orders = pd.read_excel('orders.xlsx')
# Normalize and dedupe
customers['email'] = customers['email'].str.strip().str.lower()
customers = customers.drop_duplicates(subset=['email'])
# Join and summarize
df = orders.merge(customers, on='customer_id', how='left')
sales_by_region = df.groupby('region', dropna=False)['total'].sum().reset_index()
sales_by_region.to_excel('sales_by_region.xlsx', index=False)