> ## Documentation Index > Fetch the complete documentation index at: https://proto.evodesign.org/docs/llms.txt > Use this file to discover all available pages before exploring further. # Sequence Length > Evaluate sequence length against target value or acceptable range

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Source

evo-design/proto-language/proto\_language/constraint/sequence\_composition/sequence\_length\_constraint.py

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Constraint contributors

Evaluate sequence length against target value or acceptable range. This constraint function evaluates whether sequences have appropriate lengths. It supports two modes: range mode (acceptable length window) and target mode (exact length matching). ## API Reference

ConfigSequenceLengthConfig Source

Configuration for sequence length constraint. This class defines configuration parameters for evaluating sequence length in DNA, RNA, or protein sequences. The constraint supports two modes: range mode (specify acceptable length range) and target mode (specify exact target length). Supports two mutually exclusive modes: 1. **Range mode**: Specify both min\_length and max\_length to define an acceptable length range. Sequences within this range receive score 0.0, while those outside are penalized based on distance from the range. 2. **Target mode**: Specify target\_length for exact length matching. Sequences exactly matching the target receive score 0.0, while deviations are penalized based on proportional distance from the target. Minimum acceptable length (use with max\_length for range mode) Maximum acceptable length (use with min\_length for range mode) Target length for exact matching (alternative to min/max range)

ReturnsConstraintOutput

One result per sequence. A score of 0.0 indicates the sequence meets the length requirement (within range or at target). Higher scores indicate greater deviation: * **Range mode**: Linear penalty based on distance outside \[min, max]. Score = 0.0 if within range, else proportional to deviation distance. * **Target mode**: Normalized penalty as |actual - target| / target. For example, 10% deviation from target yields score \~0.1. `metadata` carries: **For range mode:** * `length`: Integer actual sequence length * `length_mode`: String "range" * `length_min`: Integer minimum acceptable length * `length_max`: Integer maximum acceptable length **For target mode:** * `length`: Integer actual sequence length * `length_mode`: String "target" * `length_target`: Integer target length

## Usage Range mode (protein): ```python python icon="python" theme={null} >>> seqs = [(Sequence("MVLSP", "protein"),)] >>> cfg = SequenceLengthConfig(min_length=4, max_length=10) >>> results = sequence_length_constraint(seqs, cfg) ``` Target mode (DNA): ```python python icon="python" theme={null} >>> seqs = [(Sequence("ATCGATCG", "dna"),)] >>> cfg = SequenceLengthConfig(target_length=8) >>> results = sequence_length_constraint(seqs, cfg) ``` ## Metadata | Property | Value | | --------------- | ---------------------------- | | Key | `sequence-length` | | Function | `sequence_length_constraint` | | Category | `sequence_composition` | | Mode | `discrete` | | Uses GPU | `False` | | Supported Types | `dna`, `rna`, `protein` |