Function build_local_python

catalog/code/:exec/python/backend.rs:270–301

Build the Python script for local execution (no Jupyter, no IPython). Returns a script that prints exactly one line `WEFT_RESULT_JSON= ` to stdout, surrounded by whatever the user code printed. The host parses that marker line out. Dependencies are intentionally ignored: in local mode the user runs against their own Python environment and installs their own libs.

(user_code: &str, input: &Value)

/// marker line out. Dependencies are intentionally ignored: in local mode the
/// user runs against their own Python environment and installs their own libs.
fn build_local_python(user_code: &str, input: &Value) -> String {
    let (star_imports, prelude, body) = build_user_block(user_code, input);

    format!(
        r#"
import json as __weft_json__
import sys as __weft_sys__

{star_imports}

{prelude}

def __weft_user_code__():
{body}

__weft_result__ = __weft_user_code__()
if __weft_result__ is None:
    __weft_result__ = {{}}
if not isinstance(__weft_result__, dict):
    raise ValueError("Code must return a dict with output port names as keys, got: " + str(type(__weft_result__)))

# Leading \n is required so the host parser can anchor on `\n<marker>=` even
# when the user's last print() had end="" (no trailing newline). json.dumps
# default output is single-line, so the whole marker fits on one line.
__weft_sys__.stdout.write("\nWEFT_RESULT_JSON=" + __weft_json__.dumps(__weft_result__) + "\n")
__weft_sys__.stdout.flush()
"#,
        star_imports = star_imports,
        prelude = prelude,
        body = body,
    )
}

/// Build a `!pip install` line for any deps the user listed. Empty if none.
/// We don't whitelist or validate package names here: E2B is the trust boundary,