Siren for VS Code

Print-debugging for Python, without the cleanup. Write siren(x), run your code, and see the value at the end of that line in the editor. When you're done, remove every call in one click.

Nothing to pip install: the extension carries its own runtime and makes siren available to any Python program you start from a VS Code terminal or the Python debugger.

Debug

Values inline. Each siren(...) call shows its latest value at the end of its line. Hover to see the last five values (handy in loops). Every value is also logged to the Siren output channel (Siren: Show Captured Values).

user = load_user(42)
siren(user)          🧜 user = {'id': 42, 'name': 'Alex', 'plan': 'pro'}
for i in range(3):
    siren(i, label="loop")   🧜 i = 2 (last of 3)

Insert a call. Put the cursor on a variable, or select an expression, and press Ctrl+Alt+S (Cmd+Alt+S on macOS). Siren wraps the selection in siren(...), or logs the variable on a new line below, and adds from siren import siren if the file doesn't have it.

Highlighted calls. Lines with siren(...) or @siren.* decorators are tinted and marked in the scrollbar, and the status bar shows how many the current file has, so none slip into a commit.

Remove them all. Siren: Remove siren() Calls from This File (or click the status bar count) and Siren: Remove siren() Calls from Workspace delete the calls and their imports. The workspace command first lists the files that will change. A file is left as is when removing its calls would leave invalid Python, such as a loop whose only line is siren(i).

The rest of the API works too: @siren.trace logs a function's calls and return values, siren.diff(a, b) shows what changed between two objects, siren.memory() prints memory use, with siren.catch(): prints a readable traceback, and siren.breakpoint() pauses and lists local variables.

Code quality

Python files are checked when you open or save them, and the results land in the Problems panel: unused imports and functions, bare except:, pdb.set_trace() or breakpoint() left in the code, TODO and FIXME comments, and functions whose cyclomatic complexity is above 10 (configurable). Siren: Check Code Quality in Workspace checks every file at once.

.env drift

When a workspace folder has both .env and .env.example, Siren marks keys documented in .env.example but missing from .env, and keys set in .env that .env.example doesn't mention. A quick fix (Ctrl+.) adds the missing key to the other file.

Templates

Right-click a folder in the Explorer and pick New from Template... to create a script with a main(), a class, a data class, a unittest file, or a package with __init__.py, core.py and tests.

Snippets

The Siren sidebar keeps the code you reuse. Click a snippet to insert it at the cursor. Write {{name}} where a value changes: it becomes a field you fill in and move through with Tab. Select code and right-click New Snippet (from Selection) to save it. Snippets can be tagged, filtered, edited as plain files, and exported or imported as JSON.

HTTP requests

Send a request from the sidebar (New Request: method, URL, optional JSON body) and the response opens beside your code, with status and headers on top and JSON pretty-printed. Save the ones you repeat. A saved request is a JSON file you can edit, with a Send request link at the top.

How the runtime gets in

The extension adds its bundled siren package to PYTHONPATH for:

• integrated terminals opened after the extension starts (including Run Python File), and
• Python debug sessions (debugpy).

A sitecustomize module then registers siren as a builtin, so calls work even without the import. Any sitecustomize your environment already has still runs.

Programs started outside VS Code don't get the runtime, so remove the calls before you ship. Terminals that were already open when the extension started don't get it either; open a new one.

Settings

Requirements

Python 2.7 or 3.6+ on your machine. The Python extension is optional; when it's installed, Siren uses the interpreter you selected there.