Excel/Spreadsheet Processing
Reading and Analyzing Data
import pandas as pd
# Read Excel
df = pd.read_excel('file.xlsx') # Default: first sheet
all_sheets = pd.read_excel('file.xlsx', sheet_name=None) # All sheets as dict
# Analyze
df.head() # Preview data
df.info() # Column info
df.describe() # Statistics
# Write Excel
df.to_excel('output.xlsx', index=False)
Creating Excel Files with openpyxl
from openpyxl import Workbook
from openpyxl.styles import Font, PatternFill, Alignment
wb = Workbook()
sheet = wb.active
# Add data
sheet['A1'] = 'Hello'
sheet['B1'] = 'World'
sheet.append(['Row', 'of', 'data'])
# Add formula - ALWAYS use formulas, not hardcoded values
sheet['B2'] = '=SUM(A1:A10)'
# Formatting
sheet['A1'].font = Font(bold=True, color='FF0000')
sheet['A1'].fill = PatternFill('solid', start_color='FFFF00')
sheet['A1'].alignment = Alignment(horizontal='center')
# Column width
sheet.column_dimensions['A'].width = 20
wb.save('output.xlsx')
Editing Existing Files
from openpyxl import load_workbook
wb = load_workbook('existing.xlsx')
sheet = wb.active
# Modify cells
sheet['A1'] = 'New Value'
sheet.insert_rows(2)
sheet.delete_cols(3)
# Add new sheet
new_sheet = wb.create_sheet('NewSheet')
new_sheet['A1'] = 'Data'
wb.save('modified.xlsx')
Critical: Use Formulas, Not Hardcoded Values
# BAD - Hardcoding calculated values
total = df['Sales'].sum()
sheet['B10'] = total # Hardcodes 5000
# GOOD - Using Excel formulas
sheet['B10'] = '=SUM(B2:B9)'
sheet['C5'] = '=(C4-C2)/C2' # Growth rate
sheet['D20'] = '=AVERAGE(D2:D19)'
Financial Model Standards
- Blue text: Hardcoded inputs
- Black text: ALL formulas
- Green text: Links from other worksheets
- Yellow background: Key assumptions
Best Practices
- Use
data_only=True to read calculated values
- For large files: Use
read_only=True or write_only=True
- Formulas are preserved but not evaluated by openpyxl
