Python Expression

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Overview

Julep tasks support Python expressions for dynamic value computation and data manipulation. This guide explains how to use them effectively.

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The Special _ Variable

The underscore _ is a special variable that serves three different purposes depending on where it’s used:

1. First Step Input: In the first step of a task, _ contains the execution input:

# If task is executed with input `{"topic": "AI"}`
- evaluate:
    topic: _.topic  # Accesses the input "AI"

2. Previous Step Output: In any subsequent step, _ contains the output from the previous step:

- evaluate:
    results: _.split('\n')  # Splits previous step's output into lines

3. Iterator Value: In foreach and map steps, _ represents the current item being iterated.

# If the task is executed with input `{"questions": ["What is AI?", "What is Julep?"]}`
- foreach:
    in: _.questions
    do:
      - wait_for_input:
          info:
            "message": _  # _ is each question

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Where Python Expressions Are Used

Python expressions can be used in various task steps. For a complete list of step types and their syntax, refer to the Step Types table in the README.

Common places include:

• evaluate steps
• Tool arguments
• if conditions
• foreach and map iterations

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Available Functions and Libraries

The following Python functions and libraries are available for use in expressions:

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Basic Python Builtins

• abs, all, any, bool, dict, enumerate
• float, int, len, list, map, max, min
• round, set, str, sum, tuple, zip, reduce

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Safe Versions of Functions

• range: def safe_range(*args)

  Safely creates a range object with size limits (max 1,000,000 elements).

• load_json: def safe_json_loads(s: str) -> Any (Deprecated in favor of json.loads)

  Safely parses a JSON string with size limits.

• load_yaml: def safe_yaml_load(s: str) -> Any (Deprecated in favor of yaml.safe_load)

  Safely parses a YAML string with size limits.

• dump_json: def dump_json(obj: Any, *, **kwargs) -> str (Deprecated in favor of json.dumps)

  Safely serializes an object to a JSON string.

• dump_yaml: def dump_yaml(obj: Any, **kwargs) -> str (Deprecated in favor of yaml.dumps)

  Safely serializes an object to a YAML string.

• extract_json: def safe_extract_json(string: str) -> Any

  Safely extracts and parses JSON from text.

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Regex and NLP Functions

• search_regex: def search_regex(pattern: str, string: str) -> Optional[re2.Match]

  Searches for a regex pattern in a string.

• match_regex: def match_regex(pattern: str, string: str) -> bool

  Checks if a regex pattern matches a string.

• chunk_doc: def chunk_doc(string: str) -> list[str]

  Chunks a string into sentences.

• nlp pipelines.

Example using these functions in an evaluate step:

- evaluate:
    # Parse JSON string with size limit of 1MB
    data: json.loads(_.json_string)
    
    # Parse YAML string with size limit of 1MB
    config: yaml.safe_load(_.yaml_string)
    
    # Extract JSON from text that might contain markdown code blocks
    extracted_content: extract_json('Here is some JSON: ```json\n{"key": "value"}\n```')

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Standard Library Modules

• re: Regular expressions (using re2)
• json: JSON operations
• yaml: YAML operations
• string: String constants and operations
• datetime: Date and time operations
• math: Mathematical functions
• statistics: Statistical operations
• base64: Base64 encoding/decoding
• urllib.parse: URL parsing operations
• random: Random number generation
• time: Time operations

For the complete list of available functions and their safe implementations, refer to the utils.py file in the source code.

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Example Usage

Here’s a practical example combining different aspects of Python expressions:

name: Data Processing Task

main:
  # Using _ as input
  - evaluate:
      topics: _.topics  # Access input topics

  # Using _ as previous output
  - evaluate:
      filtered_topics: [t for t in _.topics if len(t) > 3]

  # Using _ in foreach
  - foreach:
      in: _.filtered_topics
      do:
        - tool: web_search
          arguments:
            query: "'Latest news about ' + _"  # _ is each topic

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Security

All Python expressions are executed in a sandboxed environment with:

This ensures safe execution while providing necessary functionality for task workflows.

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Support

If you need help with further questions in Julep:

• Join our Discord community
• Check the GitHub repository
• Contact support at hey@julep.ai