dspy.PythonInterpreter

dspy.PythonInterpreter(deno_command: list[str] | None = None, enable_read_paths: list[PathLike | str] | None = None, enable_write_paths: list[PathLike | str] | None = None, enable_env_vars: list[str] | None = None, enable_network_access: list[str] | None = None, sync_files: bool = True, tools: dict[str, Callable[..., str]] | None = None, output_fields: list[dict] | None = None)

Local interpreter for secure Python execution using Deno and Pyodide.

Implements the Interpreter protocol for secure code execution in a WASM-based sandbox. Code runs in an isolated Pyodide environment with no access to the host filesystem, network, or environment by default.

Prerequisites

Deno must be installed: https://docs.deno.com/runtime/getting_started/installation/

Examples:

# Basic execution
with PythonInterpreter() as interp:
    result = interp("print(1 + 2)")  # Returns "3"

# With host-side tools
def my_tool(question: str) -> str:
    return "answer"

with PythonInterpreter(tools={"my_tool": my_tool}) as interp:
    result = interp("print(my_tool(question='test'))")

Parameters:

Name	Type	Description	Default
deno_command	list[str] | None	command list to launch Deno.	None
enable_read_paths	list[PathLike | str] | None	Files or directories to allow reading from in the sandbox.	None
enable_write_paths	list[PathLike | str] | None	Files or directories to allow writing to in the sandbox. All write paths will also be able to be read from for mounting.	None
enable_env_vars	list[str] | None	Environment variable names to allow in the sandbox.	None
enable_network_access	list[str] | None	Domains or IPs to allow network access in the sandbox.	None
sync_files	bool	If set, syncs changes within the sandbox back to original files after execution.	True
tools	dict[str, Callable[..., str]] | None	Dictionary mapping tool names to callable functions. Each function should accept keyword arguments and return a string. Tools are callable directly from sandbox code by name.	None
output_fields	list[dict] | None	List of output field definitions for typed SUBMIT signature. Each dict should have ‘name’ and optionally ‘type’ keys.	None

Source code in .venv/lib/python3.14/site-packages/dspy/primitives/python_interpreter.py

def __init__(
    self,
    deno_command: list[str] | None = None,
    enable_read_paths: list[PathLike | str] | None = None,
    enable_write_paths: list[PathLike | str] | None = None,
    enable_env_vars: list[str] | None = None,
    enable_network_access: list[str] | None = None,
    sync_files: bool = True,
    tools: dict[str, Callable[..., str]] | None = None,
    output_fields: list[dict] | None = None,
) -> None:
    """
    Args:
        deno_command: command list to launch Deno.
        enable_read_paths: Files or directories to allow reading from in the sandbox.
        enable_write_paths: Files or directories to allow writing to in the sandbox.
            All write paths will also be able to be read from for mounting.
        enable_env_vars: Environment variable names to allow in the sandbox.
        enable_network_access: Domains or IPs to allow network access in the sandbox.
        sync_files: If set, syncs changes within the sandbox back to original files after execution.
        tools: Dictionary mapping tool names to callable functions.
               Each function should accept keyword arguments and return a string.
               Tools are callable directly from sandbox code by name.
        output_fields: List of output field definitions for typed SUBMIT signature.
               Each dict should have 'name' and optionally 'type' keys.
    """
    if isinstance(deno_command, dict):
        raise TypeError("deno_command must be a list of strings, not a dict")

    self.enable_read_paths = enable_read_paths or []
    self.enable_write_paths = enable_write_paths or []
    self.enable_env_vars = enable_env_vars or []
    self.enable_network_access = enable_network_access or []
    self.sync_files = sync_files
    self.tools = dict(tools) if tools else {}
    self.output_fields = output_fields
    self._tools_registered = False
    # TODO later on add enable_run (--allow-run) by proxying subprocess.run through Deno.run() to fix 'emscripten does not support processes' error

    if deno_command:
        self.deno_command = list(deno_command)
    else:
        args = ["deno", "run"]

        # Also allow reading Deno's cache directory so Pyodide can load its files
        deno_dir = self._get_deno_dir()
        raw_read_paths = [
            self._get_runner_path(),
            *([deno_dir] if deno_dir else []),
            *self.enable_read_paths,
            *self.enable_write_paths,
        ]
        allowed_read_paths = [_canonicalize_path(p) for p in raw_read_paths]
        args.append(f"--allow-read={','.join(allowed_read_paths)}")

        self._env_arg = ""
        if self.enable_env_vars:
            user_vars = [str(v).strip() for v in self.enable_env_vars]
            args.append("--allow-env=" + ",".join(user_vars))
            self._env_arg = ",".join(user_vars)
        if self.enable_network_access:
            args.append(f"--allow-net={','.join(str(x) for x in self.enable_network_access)}")
        if self.enable_write_paths:
            args.append(f"--allow-write={','.join(_canonicalize_path(x) for x in self.enable_write_paths)}")

        args.append(_canonicalize_path(self._get_runner_path()))

        # For runner.js to load in env vars
        if self._env_arg:
            args.append(self._env_arg)
        self.deno_command = args

    self.deno_process = None
    self._mounted_files = False
    self._request_id = 0
    self._owner_thread: int | None = None
    self._pending_large_vars = {}
    self._session_ended = False

Methods:

__call__(code: str, variables: dict[str, Any] | None = None) -> Any

Source code in .venv/lib/python3.14/site-packages/dspy/primitives/python_interpreter.py

def __call__(
    self,
    code: str,
    variables: dict[str, Any] | None = None,
) -> Any:
    return self.execute(code, variables)

execute(code: str, variables: dict[str, Any] | None = None) -> Any

Source code in .venv/lib/python3.14/site-packages/dspy/primitives/python_interpreter.py

def execute(
    self,
    code: str,
    variables: dict[str, Any] | None = None,
) -> Any:
    self._check_session_active()
    self._check_thread_ownership()
    variables = variables or {}
    code = self._inject_variables(code, variables)
    self._ensure_deno_process()
    self._mount_files()
    self._register_tools()

    for name, value in self._pending_large_vars.items():
        self._inject_large_var(name, value)

    # Send the code as JSON-RPC request
    self._request_id += 1
    execute_request_id = self._request_id
    input_data = _jsonrpc_request("execute", {"code": code}, execute_request_id)
    self._write_message(input_data, "during execution")

    # Read and handle messages until we get the final output.
    # Loop is needed because tool calls require back-and-forth communication.
    skipped = 0
    while skipped <= self._MAX_SKIP_LINES:
        output_line = self._read_response_line("during execution")
        msg = self._parse_response_line(output_line, "during execution")
        if msg is None:
            skipped += 1
            continue

        # Handle incoming requests (tool calls from sandbox)
        if "method" in msg:
            if msg["method"] == "tool_call":
                self._handle_tool_call(msg)
                continue

        # Handle success response
        if "result" in msg:
            if msg.get("id") != execute_request_id:
                self._raise_terminal_error(
                    f"Response ID mismatch: expected {execute_request_id}, got {msg.get('id')}"
                )
            result = msg["result"]
            if not isinstance(result, dict):
                self._raise_terminal_error(f"Malformed execution result: {msg}")
            self._sync_files()
            # Check for SUBMIT (encoded as success with "final" field)
            if "final" in result:
                return FinalOutput(result["final"])
            return result.get("output", None)

        # Handle error response
        if "error" in msg:
            # Errors with id=null are unsolicited errors (e.g., unhandled async rejections)
            # Treat them as errors for the current request
            if msg.get("id") is not None and msg.get("id") != execute_request_id:
                self._raise_terminal_error(
                    f"Response ID mismatch: expected {execute_request_id}, got {msg.get('id')}"
                )
            error = msg["error"]
            if not isinstance(error, dict):
                self._raise_terminal_error(f"Malformed execution error: {msg}")
            error_code = error.get("code", JSONRPC_APP_ERRORS["Unknown"])
            error_message = error.get("message", "Unknown error")
            error_data = error.get("data", {})
            if not isinstance(error_data, dict):
                self._raise_terminal_error(f"Malformed execution error data: {msg}")
            error_type = error_data.get("type", "Error")

            if error_code == JSONRPC_APP_ERRORS["SyntaxError"]:
                raise SyntaxError(f"Invalid Python syntax. message: {error_message}")
            if error_code in JSONRPC_APP_ERRORS.values():
                raise CodeExecutionError(f"{error_type}: {error_data.get('args') or error_message}")
            self._raise_terminal_error(f"{error_type}: {error_data.get('args') or error_message}")

        # Unexpected message format - neither a recognized method nor a response
        self._raise_terminal_error(f"Unexpected message format from sandbox: {msg}")

    self._raise_terminal_error(f"Too many non-JSON lines ({skipped}) during execution")

shutdown() -> None

Source code in .venv/lib/python3.14/site-packages/dspy/primitives/python_interpreter.py

def shutdown(self) -> None:
    session_was_active = not self._session_ended
    self._session_ended = True
    if self.deno_process and self.deno_process.poll() is None:
        if session_was_active:
            self.deno_process.stdin.write(_jsonrpc_notification("shutdown") + "\n")
            self.deno_process.stdin.flush()
            self.deno_process.stdin.close()
        else:
            self.deno_process.terminate()
        self.deno_process.wait()
    self.deno_process = None
    self._owner_thread = None

start() -> None

Initialize the Deno/Pyodide sandbox.

This pre-warms the sandbox by starting the Deno subprocess. Can be called explicitly for pooling, or will be called lazily on first execute().

Idempotent while the session is active. A stopped or shut-down session cannot be restarted because its Python state cannot be reconstructed.

Source code in .venv/lib/python3.14/site-packages/dspy/primitives/python_interpreter.py

def start(self) -> None:
    """Initialize the Deno/Pyodide sandbox.

    This pre-warms the sandbox by starting the Deno subprocess.
    Can be called explicitly for pooling, or will be called lazily
    on first execute().

    Idempotent while the session is active. A stopped or shut-down session
    cannot be restarted because its Python state cannot be reconstructed.
    """
    self._ensure_deno_process()