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Salary calculator

A console program that works out the gross and net pay of a month from the hourly wage.

Goal

Write a program that calculates something useful, with input, conditions and loops.

Implementation

Grew over three versions: from a plain calculator to asking for working hours, working days, year and month.
The program counts the working days of the chosen month itself with the calendar module.
Simplified deductions: payroll tax in steps, church tax depending on the state and social insurance with contribution ceilings.
Wrong input is caught and asked for again.

Code

From gross to net in a few lines

payroll.py

def payroll_tax(monthly):
    if monthly < 1000:
        payroll_tax = 5
    elif 1000 <= monthly < 2000:
        payroll_tax = 15
    elif 2000 <= monthly < 3500:
        payroll_tax = 25
    elif 3500 <= monthly < 5000:
        payroll_tax = 35
    elif 5000 <= monthly < 7000:
        payroll_tax = 42
    else:
        payroll_tax = 45

    netto = monthly * (1 - payroll_tax / 100)
    return netto

netto = payroll_tax(monthly)

churchtax_netto = (monthly - netto) * churchtax

pension_insurance_limit = 7550
health_insurance_limit = 5175

if monthly < pension_insurance_limit:
    pension_insurance = monthly * .093
    unemployment_insurance = monthly * .013
else:
    pension_insurance = pension_insurance_limit * .093
    unemployment_insurance = pension_insurance_limit * .013

if monthly < health_insurance_limit:
    health_insurance = monthly * .073
    nursingcare_insurance = monthly * .023
else:
    health_insurance = health_insurance_limit * .073
    nursingcare_insurance = health_insurance_limit * .023

One function picks the tax rate by steps; social insurance is capped at the contribution ceiling.

What I learned

Never trust input. And a program grows better in small versions than in one big go.