Parameter Iterators (piter)

The piter operator provides a lightweight, composable way to create parameter sweeps using simple dictionaries and operators. Unlike the Sweep class which requires @proto decorated classes, piter works with plain dictionaries and supports lazy evaluation for memory efficiency.

Syntax: `piter @ {...}`

params-proto uses the @ operator for clean, readable parameter iteration:

python

# Preferred syntax (v3.0.0+)
configs = piter @ {"lr": [0.001, 0.01], "batch_size": [32, 64]}

# Legacy syntax (still supported for backward compatibility)
configs = piter({"lr": [0.001, 0.01], "batch_size": [32, 64]})

Both syntaxes are fully functional, but @ is preferred for cleaner, more readable code.

Operators Quick Reference

Operator	Name	Description	Example	Result
`@`	Create	Create iterator from dict	`piter @ {"lr": [0.001, 0.01]}`	2 configs
`*`	Product	Cartesian product	`piter @ {"lr": [0.001, 0.01]} * {"bs": [32, 64]}`	4 configs (2×2)
`%`	Override	Add fixed params to all	`configs % {"seed": 42}`	Same count, +seed
`**`	Repeat	Repeat each config n times	`configs ** 3`	3× count

Operator Precedence

@ and * have the same precedence (both are multiplicative), evaluated left-to-right:

python

# This works - evaluated as ((piter @ {...}) * {...}) * {...}
piter @ {"lr": [0.001, 0.01]} * {"bs": [32, 64]} * {"seed": [1, 2]}

# Parentheses needed for % and ** in complex expressions
(piter @ {"lr": [0.001, 0.01]} * {"bs": [32, 64]}) % {"device": "cuda"}
(piter @ {"lr": [0.001, 0.01]}) ** 3

Precedence order (high to low): ** (power) > @ * (same level) > % (modulo)

python

# These are equivalent:
piter @ {"lr": [0.001, 0.01]} * {"bs": [32, 64]} % {"seed": 42}
((piter @ {"lr": [0.001, 0.01]}) * {"bs": [32, 64]}) % {"seed": 42}

# Power binds tighter than product:
piter @ {"lr": [0.001, 0.01]} ** 3 * {"bs": [32, 64]}  # Error! ** binds first
(piter @ {"lr": [0.001, 0.01]}) ** 3 * {"bs": [32, 64]}  # Correct: 6 * 2 = 12 configs

Quick Start

python

from params_proto.hyper import piter

# Create a parameter sweep from a dictionary (zips by default)
configs = piter @ {"lr": [0.001, 0.01], "batch_size": [32, 64]}

# Iterate over zipped configurations (2 configs)
for config in configs:
    print(config)
    # {'lr': 0.001, 'batch_size': 32}
    # {'lr': 0.01, 'batch_size': 64}

# For Cartesian product, use the * operator (only first needs piter @)
configs = piter @ {"lr": [0.001, 0.01]} * {"batch_size": [32, 64]}
# This creates 4 configs: all combinations

Key Features

Lazy evaluation: Configurations are generated on-the-fly, not stored in memory
Composable: Combine iterators using operators (*, %, **)
Reusable: Results are cached, so you can iterate multiple times
Memory efficient: Only materializes when needed via .to_list() or len()

Basic Usage

Creating a piter

python

# Lists of values are zipped element-wise (default behavior)
configs = piter @ {
    "lr": [0.001, 0.01, 0.1],
    "batch_size": [32, 64, 128]
}
# Produces 3 configs (zipped): (0.001, 32), (0.01, 64), (0.1, 128)

# Single values
fixed = piter @ {"seed": 42, "epochs": 100}
# Produces 1 config

# For Cartesian product, use * operator (only first needs piter @)
configs = piter @ {"lr": [0.001, 0.01, 0.1]} * {"batch_size": [32, 64]}
# Produces 6 configs (3 × 2)

# With prefixes for multiple parameter groups (zipped)
configs = piter @ {
    "model.depth": [18, 50],
    "training.lr": [0.001, 0.01]
}
# Produces 2 configs (zipped)

Materializing Configs

python

# Lazy iteration (recommended)
for config in configs:
    train(config)

# Convert to list (materializes all configs)
config_list = configs.to_list()
# or
config_list = configs.list

# Get length (materializes internally)
num_configs = len(configs)

Operators

Cartesian Product (`*`)

Combine parameter iterators to create all possible combinations. When chaining multiple dicts, only the first needs piter @:

python

# Preferred: chain with * operator (only first needs piter @)
combined = piter @ {"lr": [0.001, 0.01]} * {"batch_size": [32, 64]}

list(combined)
# [
#   {'lr': 0.001, 'batch_size': 32},
#   {'lr': 0.001, 'batch_size': 64},
#   {'lr': 0.01, 'batch_size': 32},
#   {'lr': 0.01, 'batch_size': 64}
# ]

# Also works: separate piter @ for each (legacy style)
piter1 = piter @ {"lr": [0.001, 0.01]}
piter2 = piter @ {"batch_size": [32, 64]}
combined = piter1 * piter2  # Same result

Use case: Exploring all combinations of independent hyperparameters.

Override (`%`)

Apply fixed parameters to all configurations:

python

# Create configs with Cartesian product
configs = piter @ {"lr": [0.001, 0.01]} * {"batch_size": [32, 64]}

# Override with a dict
with_seed = configs % {"seed": 42, "device": "cuda"}

list(with_seed)
# [
#   {'lr': 0.001, 'batch_size': 32, 'seed': 42, 'device': 'cuda'},
#   {'lr': 0.001, 'batch_size': 64, 'seed': 42, 'device': 'cuda'},
#   {'lr': 0.01, 'batch_size': 32, 'seed': 42, 'device': 'cuda'},
#   {'lr': 0.01, 'batch_size': 64, 'seed': 42, 'device': 'cuda'}
# ]

# Override with another piter (uses first config)
with_defaults = configs % (piter @ {"seed": 42, "device": "cuda"})

Use case: Adding fixed parameters (seed, device, logging config) to all experiments.

Repeat (`**`)

Repeat each configuration n times:

python

configs = piter @ {"lr": [0.001, 0.01]}

repeated = configs ** 3

list(repeated)
# [
#   {'lr': 0.001},
#   {'lr': 0.001},
#   {'lr': 0.001},
#   {'lr': 0.01},
#   {'lr': 0.01},
#   {'lr': 0.01}
# ]

Use case: Running multiple trials/seeds for each configuration.

Composition Patterns

Pattern 1: Grid Search with Fixed Seed

python

# Grid search over hyperparameters (chain with * for Cartesian product)
grid = (
    piter @ {"lr": [0.001, 0.01, 0.1]}
    * {"batch_size": [32, 64, 128]}
    * {"weight_decay": [0.0, 0.0001, 0.001]}
)

# Add fixed seed to all configs
experiments = grid % {"seed": 42}

# 27 configs (3 × 3 × 3), all with seed=42

Pattern 2: Multiple Trials per Config

python

# Define hyperparameter search space (Cartesian product)
configs = piter @ {"lr": [0.001, 0.01]} * {"batch_size": [32, 64]}

# Run 5 trials per config with different seeds
trials = configs ** 5

# 20 total runs (4 configs × 5 trials)

Pattern 3: Combining Multiple Parameter Groups

python

# Model architecture variations
models = piter @ {"model.type": ["resnet18", "resnet50", "vit"]}

# Training hyperparameters (chain with * for Cartesian product)
training = piter @ {"training.lr": [0.001, 0.01]} * {"training.batch_size": [32, 64]}

# All combinations
experiments = models * training

# 12 configs (3 models × 2 lr × 2 batch_size)

Pattern 4: Chained Composition

python

# Build complex sweep by chaining operators (only first needs piter @)
experiments = ((
    piter @ {"model": ["resnet", "vit"]}
    * {"lr": [0.001, 0.01]}
    * {"batch_size": [32, 64]}
) % {"seed": 42, "device": "cuda"}) ** 3

# 24 total runs (2 × 2 × 2 = 8 configs, 3 trials each)

Integration with Sweep

The Sweep class also supports piter operators:

python

from params_proto import proto, Sweep
from params_proto.hyper import piter

@proto
class Config:
    lr: float = 0.001
    batch_size: int = 32

# Create sweep the traditional way
sweep = Sweep(Config)
with sweep.product:
    Config.lr = [0.001, 0.01]
    Config.batch_size = [32, 64]

# Use operators on Sweep objects
with_seed = sweep % {"seed": 42}
repeated = sweep ** 3

# Can also mix Sweep with piter
combined = sweep * (piter @ {"optimizer": ["adam", "sgd"]})

Comparison: piter vs Sweep

Feature	`piter`	`Sweep`
Input	Plain dictionaries	`@proto` decorated classes
Syntax	`piter @ {"lr": [0.001, 0.01]}`	`with sweep.product: Config.lr = [0.001, 0.01]`
Default behavior	Zip (element-wise)	Context-dependent (`.product`, `.zip`, etc.)
Operators	`` (product), `%` (override), `*` (repeat)	Context managers (`.product`, `.zip`, `.set`)
Lazy	Yes	No (materializes in context)
Type checking	No	Yes (via `@proto`)
Proto integration	No	Yes (updates class attributes)
Use case	Quick sweeps, scripting	Production configs, type safety

Best Practices

1. Use descriptive keys

python

# Good: Clear parameter names with prefixes
piter @ {
    "model.depth": [18, 50],
    "training.lr": [0.001, 0.01],
    "training.optimizer": ["adam", "sgd"]
}

# Avoid: Ambiguous names
piter @ {"d": [18, 50], "l": [0.001, 0.01]}

2. Materialize only when necessary

python

# Good: Iterate lazily
for config in experiments:
    train(config)

# Avoid: Unnecessary materialization
all_configs = experiments.to_list()  # Uses memory
for config in all_configs:
    train(config)

3. Use operators for clarity

python

# Good: Use * for Cartesian product (only first needs piter @)
grid = piter @ {"lr": [0.001, 0.01]} * {"batch_size": [32, 64]}
# 4 configs: all combinations

# Good: Use zip (default) for related parameters
paired = piter @ {"lr": [0.001, 0.01], "weight_decay": [0.0001, 0.001]}
# 2 configs: (0.001, 0.0001) and (0.01, 0.001)

# Good: Use % for fixed values
with_defaults = (piter @ {"lr": [0.001, 0.01]}) % {"seed": 42, "device": "cuda"}

# Avoid: Mixing independent parameters in single dict (implicit zip)
mixed = piter @ {"lr": [0.001, 0.01], "batch_size": [32, 64]}
# Only 2 configs (zipped), might not be what you want for grid search

4. Combine with type-safe configs in production

python

from params_proto import proto
from params_proto.hyper import piter

@proto
class Config:
    lr: float = 0.001
    batch_size: int = 32
    seed: int = 42

# Use piter for sweep definition (Cartesian product for grid search)
sweep_configs = (
    piter @ {"lr": [0.001, 0.01, 0.1]}
    * {"batch_size": [32, 64]}
) % {"seed": 42}

# Apply to typed config
for overrides in sweep_configs:
    Config._update(overrides)
    train()  # Config.lr, Config.batch_size are type-checked

Advanced Examples

Conditional Parameter Sweeps

python

# Different learning rates for different optimizers
adam_configs = piter @ {"optimizer": "adam"} * {"lr": [0.0001, 0.001, 0.01]}

sgd_configs = (
    piter @ {"optimizer": "sgd"}
    * {"lr": [0.01, 0.1, 1.0]}
    * {"momentum": [0.9, 0.95]}
)

# Combine into single sweep (use list concatenation)
all_configs = adam_configs.to_list() + sgd_configs.to_list()
# 3 adam configs + 6 sgd configs = 9 total

Nested Grids with Fixed Outer Parameters

python

# Coarse grid
coarse = piter @ {"lr": [0.001, 0.01, 0.1]}

# For each coarse lr, fine-tune batch size
fine_tuned = []
for coarse_config in coarse:
    fine = (piter @ {"batch_size": [16, 32, 64, 128]}) % coarse_config
    fine_tuned.extend(fine.to_list())

# 12 total configs (3 lr × 4 batch_size)

Hierarchical Parameter Groups

python

# Dataset variations
datasets = piter @ {"data.name": ["cifar10", "cifar100", "imagenet"]}

# Model architectures per dataset
cifar_models = piter @ {"model.type": ["resnet18", "resnet34"]}
imagenet_models = piter @ {"model.type": ["resnet50", "resnet101"]}

# Training configs
training = piter @ {"training.lr": [0.001, 0.01]}

# Compose based on dataset
cifar10_exps = piter @ {"data.name": "cifar10"} * cifar_models * training
cifar100_exps = piter @ {"data.name": "cifar100"} * cifar_models * training
imagenet_exps = piter @ {"data.name": "imagenet"} * imagenet_models * training

# Combine all
all_experiments = (
    cifar10_exps.to_list() +
    cifar100_exps.to_list() +
    imagenet_exps.to_list()
)

API Reference

`piter @ spec` or `piter(spec: dict) -> ParameterIterator`

Create a parameter iterator from a specification dictionary.

Syntax:

python

# Preferred (v3.0.0+)
configs = piter @ {"lr": [0.001, 0.01]}

# Legacy (still supported)
configs = piter({"lr": [0.001, 0.01]})

Args:

spec: Dict mapping parameter names (strings) to values or lists of values

Returns:

ParameterIterator that zips parameter lists element-wise

Note: For Cartesian product, use the * operator to chain multiple dicts. Only the first needs piter @:

python

configs = piter @ {"lr": [0.001, 0.01]} * {"batch_size": [32, 64]}

`ParameterIterator` Methods

Method	Description
`__iter__()`	Iterate over configurations
`to_list()`	Materialize all configs to a list
`.list`	Property alias for `to_list()`
`__len__()`	Return number of configs (materializes)
`__mul__(other)`	Cartesian product with another iterator (`*`)
`__mod__(other)`	Apply overrides to all configs (`%`)
`__pow__(n)`	Repeat each config n times (`**`)

Core Concepts - Decorators and basic usage
Configuration Patterns - Function vs class configurations
CLI Fundamentals - Basic CLI features
Parameter Overrides - Override methods and context managers
Hyperparameter Sweeps - Traditional Sweep class with @proto integration
Advanced Patterns - Prefixes and composition

Parameter Iterators (piter)

Syntax: piter @ {...}

Operators Quick Reference

Operator Precedence

Quick Start

Key Features

Basic Usage

Creating a piter

Materializing Configs

Operators

Cartesian Product (*)

Override (%)

Repeat (**)

Composition Patterns

Pattern 1: Grid Search with Fixed Seed

Pattern 2: Multiple Trials per Config

Pattern 3: Combining Multiple Parameter Groups

Pattern 4: Chained Composition

Integration with Sweep

Comparison: piter vs Sweep

Best Practices

1. Use descriptive keys

2. Materialize only when necessary

3. Use operators for clarity

4. Combine with type-safe configs in production

Advanced Examples

Conditional Parameter Sweeps

Nested Grids with Fixed Outer Parameters

Hierarchical Parameter Groups

API Reference

piter @ spec or piter(spec: dict) -> ParameterIterator

ParameterIterator Methods

Related

Syntax: `piter @ {...}`

Cartesian Product (`*`)

Override (`%`)

Repeat (`**`)

`piter @ spec` or `piter(spec: dict) -> ParameterIterator`

`ParameterIterator` Methods