PolicyEngine Code Organization

Patterns for organizing PolicyEngine code - naming conventions, folder structure, and file organization.

Using the Variable Prefix

The variable prefix is defined in sources/working_references.md.

Look for this section:

## Official Program Name

**Federal Program**: [Federal program name]
**State's Official Name**: [State's official name]
**Abbreviation**: [Abbreviation]
**Source**: [Legal citation]

**Variable Prefix**: `[state]_[abbreviation]`

Use this prefix for all variable and parameter names.

---

Variable Naming Patterns

State Programs

# Pattern: {state}_{program}
az_liheap      # Arizona LIHEAP
ca_calfresh    # California CalFresh (SNAP)
ny_heap        # New York HEAP (LIHEAP)
ma_snap        # Massachusetts SNAP (uses federal name)

# Sub-variables: {state}_{program}_{component}
az_liheap_eligible
az_liheap_income_eligible
az_liheap_benefit_amount

Federal Programs

# Pattern: just {program}
snap
liheap
wic

# Sub-variables: {program}_{component}
snap_eligible
snap_gross_income
liheap_eligible

---

Standard Variable Components

Use these standard suffixes with your variable prefix:

Eligibility Variables

{prefix}_eligible              # Final eligibility (combines all checks)
{prefix}_income_eligible       # Income eligibility
{prefix}_resource_eligible     # Resource/asset eligibility
{prefix}_activity_eligible     # Work/activity requirement eligibility
{prefix}_categorical_eligible  # Categorical eligibility
{prefix}_demographic_eligible  # Age, household composition eligibility
{prefix}_immigration_eligible  # Immigration status eligibility

Calculation Variables

{prefix}                       # Final benefit amount
{prefix}_maximum_benefit       # Maximum possible benefit
{prefix}_countable_income      # Income after deductions
{prefix}_countable_earned_income
{prefix}_countable_unearned_income
{prefix}_gross_income          # Total income before deductions

Deduction/Disregard Variables

{prefix}_earned_income_disregard
{prefix}_work_expense_deduction
{prefix}_dependent_care_deduction
{prefix}_standard_deduction

Threshold/Limit Variables

{prefix}_income_limit
{prefix}_resource_limit
{prefix}_payment_standard
{prefix}_need_standard         # Use state's terminology

---

State-Specific Terminology

Use the terminology from sources/working_references.md.

States use different terms for the same concepts:

Concept	Possible Terms	Example
Benefit amount	Payment Standard, Need Standard, Grant Amount	{prefix}_need_standard
Income threshold	Gross Income Limit, GMI, Countable Income Limit	{prefix}_gmi_limit
Earnings deduction	Earned Income Disregard, Work Expense Deduction	{prefix}_earned_income_disregard

Match the exact terms from the documentation.

---

Folder Organization Principles

Core Principles

1. Group logically - Files that relate to the same aspect should be together
2. Don't create subfolder for 1 file - If only 1 file for an aspect, keep it at parent level
3. Final output at root - The main benefit variable (e.g., {prefix}.py) stays at the program folder root

Common Aspects (adapt to your program)

• income/ - Income calculations, limits, deductions
• eligibility/ - Eligibility checks
• resources/ - Asset/resource calculations
• deductions/ - Deductions and disregards

Study Existing Implementations

Each program is different. Before organizing, look at similar programs in the codebase:

ls policyengine_us/variables/gov/states/{state}/{agency}/

---

Folder Structure Patterns

Small Program (~5 files) - Keep Flat

policyengine_us/variables/gov/states/{state}/{agency}/{program}/
├── {prefix}.py                    # Final benefit (at root)
├── {prefix}_eligible.py
├── {prefix}_income_eligible.py
├── {prefix}_maximum_benefit.py
└── {prefix}_countable_income.py

Medium Program (6-15 files) - Light Organization

policyengine_us/variables/gov/states/{state}/{agency}/{program}/
├── {prefix}.py                    # Final benefit (at root)
├── eligibility/
│   ├── {prefix}_eligible.py
│   ├── {prefix}_income_eligible.py
│   └── {prefix}_resource_eligible.py
└── income/
    ├── {prefix}_countable_income.py
    └── {prefix}_gross_income.py

Large Program (>15 files) - Full Structure

policyengine_us/variables/gov/states/{state}/{agency}/{program}/
├── {prefix}.py                    # Final benefit (at root)
├── eligibility/
│   ├── {prefix}_eligible.py
│   ├── {prefix}_income_eligible.py
│   ├── {prefix}_resource_eligible.py
│   └── {prefix}_demographic_eligible.py
├── income/
│   ├── {prefix}_countable_income.py
│   ├── {prefix}_countable_earned_income.py
│   └── {prefix}_gross_income.py
└── deductions/
    ├── {prefix}_earned_income_disregard.py
    └── {prefix}_work_expense_deduction.py

Tests

policyengine_us/tests/policy/baseline/gov/states/{state}/{agency}/{program}/
├── {prefix}.yaml
├── {prefix}_eligible.yaml
├── {prefix}_income_eligible.yaml
└── integration.yaml          # Always named integration.yaml

---

Parameter Folder Organization

Parameter folders follow similar principles to variable folders — group by function.

Keep folders focused on their purpose

Each subfolder should contain parameters that serve the same function. Don't use a folder as a catch-all.

# ❌ BAD — eligibility/ contains rate dimension boundaries that aren't eligibility criteria
ccap/
├── eligibility/
│   ├── income_limit.yaml           # ✅ Eligibility
│   ├── child_age_threshold.yaml    # ✅ Eligibility
│   ├── center_infant_max_months.yaml  # ❌ Rate table age group boundary
│   ├── preschool_max_years.yaml       # ❌ Rate table age group boundary
│   └── time_category.yaml            # ❌ Authorization concept
└── rates/

# ✅ GOOD — each folder contains parameters that match its purpose
ccap/
├── age_groups/                     # Age group boundaries for rate lookups
│   ├── center_infant_max_months.yaml
│   └── preschool_max_years.yaml
├── eligibility/                    # Actual eligibility criteria
│   ├── income_limit.yaml
│   └── child_age_threshold.yaml
├── rates/
└── time_category.yaml              # At root — doesn't fit neatly in a subfolder

The key question: "Is this parameter an eligibility rule, a rate-table dimension boundary, a benefit calculation input, or something else?" Put it in the folder that matches its function.

---

Common Mistakes to Avoid

Variable Names

# ❌ WRONG - Using federal name when state has official name
ca_tanf_eligible          # California calls it CalWORKs

# ✅ CORRECT - Using state's official name
ca_calworks_eligible

# ❌ WRONG - Inconsistent naming
az_liheap_benefit
az_liheap_eligible_status  # Should be az_liheap_eligible

# ✅ CORRECT - Consistent pattern
az_liheap
az_liheap_eligible

Test File Names

# ❌ WRONG - Prefixed integration test
az_liheap_integration.yaml

# ✅ CORRECT - Standard integration test name
integration.yaml

# ❌ WRONG - Descriptive test names
test_low_income_family.yaml

# ✅ CORRECT - Variable-based test names
az_liheap.yaml
az_liheap_eligible.yaml