# PySnooper — Never Use Print for Python Debugging Again

> A debugging tool that lets you trace Python function execution by adding a single decorator. See every line executed, local variable changes, and return values without setting breakpoints.

## Install

Save as a script file and run:

# PySnooper — Never Use Print for Python Debugging Again

## Quick Use
```bash
pip install pysnooper
```
```python
import pysnooper

@pysnooper.snoop()
def calculate(x, y):
    result = x * y + 1
    return result
```

## Introduction
PySnooper is a poor man's debugger for Python. Instead of painstakingly adding print statements or configuring a full debugger, you decorate a function with `@pysnooper.snoop()` and get a complete trace of every line executed, every variable modified, and every return value.

## What PySnooper Does
- Traces function execution line by line with a single decorator
- Logs all local variable assignments and their new values
- Shows elapsed time for each traced line
- Supports writing trace output to files or custom streams
- Allows watching specific expressions and nested function calls

## Architecture Overview
PySnooper hooks into Python's `sys.settrace` mechanism. When a decorated function runs, the tracer intercepts each line event, inspects the local namespace for changes, formats the output, and writes it to stderr or a specified file. The `@pysnooper.snoop()` decorator wraps the target function transparently, so no changes to the function body are needed.

## Self-Hosting & Configuration
- Install with pip: `pip install pysnooper`
- Apply `@pysnooper.snoop()` to any function you want to trace
- Write traces to a file: `@pysnooper.snoop("/tmp/debug.log")`
- Watch specific expressions: `@pysnooper.snoop(watch=("len(items)", "self.count"))`
- Trace deeper calls: `@pysnooper.snoop(depth=2)` to follow nested function invocations

## Key Features
- Zero-config debugging with a single decorator
- Traces variable changes without manual print statements
- Supports conditional tracing with `watch` and `watch_explode`
- Thread-safe with per-thread trace output
- Lightweight with no dependencies beyond the Python standard library

## Comparison with Similar Tools
- **print()** — Requires manual placement and removal; PySnooper automates the entire trace
- **pdb / breakpoint()** — Interactive debugger requiring stepping; PySnooper is non-interactive and logs everything
- **icecream (ic)** — Focused on inspect-style printing; PySnooper traces full execution flow
- **Hunter** — More powerful tracing framework; PySnooper is simpler for quick debugging

## FAQ
**Q: Does PySnooper slow down my code?**
A: Yes, tracing adds overhead. Use it only during development and debugging, not in production. Remove the decorator when done.

**Q: Can I use PySnooper with async functions?**
A: PySnooper works with synchronous functions. For async code, consider alternatives like `snoop` (a fork) or logging-based approaches.

**Q: How do I trace only certain variables?**
A: Use the `watch` parameter: `@pysnooper.snoop(watch=("my_var",))` to track specific expressions alongside the default local variable tracing.

**Q: Can I integrate PySnooper with logging?**
A: Yes. Pass a logging handler or file object as the output target: `@pysnooper.snoop(output=my_logger)`.

## Sources
- [GitHub Repository](https://github.com/cool-RR/PySnooper)
- [PyPI Package](https://pypi.org/project/PySnooper/)

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Source: https://tokrepo.com/en/workflows/asset-6f5466b0
Author: Script Depot