Siren

Minimal Python debug helper with automatic cleanup.

A tiny debugging utility for Python that prints variables with file/line context, traces function calls, measures execution time, and safely removes debug calls from your code.

Install

pip install siren-debug

The package also installs two commands: siren-clean (remove debug calls) and siren-autoload (use siren without importing it).

Quick Start

from siren import siren

x = 10
user = {"name": "Alex", "items": [1, 2, 3]}

siren(x)
siren(user)

[🧜‍ SIREN core.py:10] x = 10
[🧜‍ SIREN core.py:11] user = {'name': 'Alex', 'items': [1, 2, 3]}

Siren automatically uses pprint for complex objects, and picks up the file/line it was called from.

Features

• Works with Python 2.7 and 3.6+
• Zero external dependencies
• Prints values with file and line number
• Uses pprint automatically for complex data
• Function tracing with @siren.trace, object diffing with siren.diff, and an interactive siren.breakpoint()
• Quiet mode, conditional logging, and file logging
• Removes siren(...) calls automatically with siren-clean
• Use siren anywhere without importing it via siren-autoload
• Works in scripts, CLI tools, Django, Flask, FastAPI, and more
• Colored output with emoji for easy visual scanning

Usage

Call siren(...) with one or more values. It returns them unchanged, so it can be inlined:

from siren import siren

siren(x, data, user)
result = siren(compute())  # still returns compute()'s value

Label — tag a call for easier scanning:

siren(value, label="BEFORE SAVE")

Timer — measure execution time for a call:

siren(x, timeit=True)
# [🧜‍ SIREN core.py:10] x = 10
# [🧜‍ SIREN TIME] 0.000123s

Quiet mode — suppress output without removing the call:

siren(x, quiet=True)      # this call only, still returns x
siren.set_quiet(True)     # every call, until set_quiet(False)

Conditional logging — only print when a condition holds:

siren(x, if_equals=5)        # only if x == 5
siren(items, if_len_gt=100)  # only if len(items) > 100
siren(items, if_len_lt=5)    # only if len(items) < 5
siren(result, if_true=True)  # only if result is truthy
siren(error, if_false=True)  # only if error is falsy

Logging to file — mirror output to a file:

siren.set_logfile("debug.log")
siren(x)  # prints to stdout AND writes to debug.log

Inspect configuration:

config = siren.get_config()
print(config)  # {"quiet": False, "logfile": None, "enabled": True}

Function tracing

@siren.trace logs a function's calls, arguments, return value, execution time, and exceptions automatically:

from siren import trace

@siren.trace
def add(a, b):
    return a + b

add(2, 3)

[🧜‍ SIREN core.py:10] Calling add(a=2, b=3)
[🧜‍ SIREN core.py:11] Returned from add -> 5 [int] (0.000123s)

Configuration options (all default to True):

@siren.trace(timeit=True, show_args=False, show_type=False)
def multiply(a, b):
    return a * b

Exceptions are logged before being re-raised, so @siren.trace never swallows an error:

@siren.trace
def divide(a, b):
    return a / b

divide(5, 0)  # Logs exception before raising

Diff and breakpoint

siren.diff compares two dicts, lists, tuples, or any comparable objects:

before = {"name": "Alice", "age": 30}
after = {"name": "Alice", "age": 31, "city": "NYC"}

siren.diff(before, after)

[🧜‍ SIREN test.py:10] DIFF
[🧜‍ SIREN test.py:11] [~] age: 30 → 31 (changed)
[🧜‍ SIREN test.py:12] [+] city: NYC (new)

siren.breakpoint() pauses execution and prints local variables:

x = 42
data = {"items": [1, 2, 3]}

siren.breakpoint()  # Pauses and displays all locals
# Press Ctrl+C to continue, or type 'd' to drop into pdb

Cleaning debug calls

Run siren-clean in a project folder to remove all siren(...) calls and their import lines — comments and string literals are left untouched:

siren-clean

Before:

from siren import siren
siren(x)
print("hello")
siren(data)

After:

print("hello")

Autoload (no per-file imports)

By default you still need from siren import siren in every file that uses it. If you'd rather call siren(x) anywhere in a project without importing it each time, enable autoload once per environment (virtualenv, Docker image, CI job, etc.):

siren-autoload on
siren-autoload status   # check whether it's enabled
siren-autoload off      # disable again

This writes a .pth file into the current environment's site-packages, injecting siren into Python's builtins as soon as any interpreter starts in that environment — no import needed anywhere, including in Django apps, Flask views, scripts, or the shell. It's opt-in per environment, so it won't silently affect environments where you didn't run on.

Framework examples

from django.http import JsonResponse
from siren import siren

def my_view(request):
    user_data = request.GET.dict()
    siren(user_data, label="REQUEST_PARAMS")

    result = process_data(user_data)
    siren(result)

    return JsonResponse(result)

from flask import Flask, request
from siren import siren, trace

app = Flask(__name__)

@app.route("/api/users")
def get_users():
    query = request.args.get("q")
    siren(query, label="SEARCH_QUERY")

    users = search_users(query)
    return {"users": users}

@siren.trace
def search_users(query):
    # Function entry/exit will be logged automatically
    return [{"id": 1, "name": "Alice"}]

from fastapi import FastAPI
from siren import siren, trace

app = FastAPI()

@app.get("/items/{item_id}")
async def get_item(item_id: int, q: str = None):
    siren({"item_id": item_id, "q": q}, label="QUERY_PARAMS")

    item = await fetch_item(item_id)
    return item

@siren.trace(timeit=True)
async def fetch_item(item_id: int):
    # Execution time and arguments will be logged
    return {"id": item_id, "name": "Item"}

Why use Siren?

Debug prints are easy to add, but hard to remove later. Siren gives you a fast debug workflow and a safe cleanup step so your temporary debug code does not stay in production.

Project

• Package name: siren-debug
• Python versions: 2.7, 3.6+
• License: MIT
• PyPI: https://pypi.org/project/siren-debug/

License

MIT