LogEye

Understand exactly what your code is doing in real time, no debugger needed.

LogEye is a frictionless runtime logger for Python that shows variable changes, function calls, and data mutations as they happen.

Think of it as "print debugging" just better - automated, structured, easy to drop into, and remove from any codebase

Installation

pip install logeye

Quick example

from logeye import log

@log
def add(a, b):
	return a + b

add(2, 3)

@log(mode="edu")
def add_edu(a, b):
	return a + b

add_edu(2, 3)

Output:

[0.000s] playground.py:7 (call) add = {'args': (2, 3), 'kwargs': {}}
[0.000s] playground.py:5 (set) add.a = 2
[0.000s] playground.py:5 (set) add.b = 3
[0.000s] playground.py:5 (return) add = 5
[0.000s] Calling add_edu(2, 3)
[0.000s] a = 2
[0.000s] b = 3
[0.000s] add_edu(2, 3) returned 5

Table of Contents

• Who is it for
• What does it do
• Quick start
• Educational Mode
  • Before vs After
  • What changes in educational mode
  • Example - Educational Factorial
• Logging functions
• Advanced function logging
• Logging objects
• Messages
• Utility functions
• Output format
• Some Usage Examples
• Inspiration
• Limitations
• Contact
• License

Who is it for

LogEye helps you see how your code executes step by step.

Perfect for:

• beginners learning programming
• students studying algorithms
• teachers explaining concepts

No more scattered print() calls. No debugger setup. Just run your code and see everything.

What does it do

Core features:

• educational mode for algorithm tracing
• log values with automatic variable name inference
• trace function calls, local variables, and returns
• track object and data structure mutations in real time
• format messages using f-string, template, or scope variables

Advanced features:

• filter variables and control verbosity (level, filter)
• log to files or stdout
• recursively track nested structures
• AST-based name inference (including multi-line assignments)

However, keep in mind that name inference is best-effort and may not be accurate in some more extreme cases.

Quick start

from logeye import log

x = log(10)
message = log("Hello from {name}", name="Matt")


@log(level="call")
def add(a, b):
	something = 2 + 2
	return a + b


add(2, 2)

name = "Matt"
message2 = log("Hello from $name")

config = log({"debug": True, "port": 8080})
config.port = 9090
config["debug"] = False

Example output:

[0.000s] playground.py:3 (set) x = 10
[0.000s] playground.py:4 (set) message = 'Hello from Matt'
[0.000s] playground.py:13 (call) add = {'args': (2, 2), 'kwargs': {}}
[0.000s] playground.py:10 (return) add = 4
[0.000s] playground.py:16 (set) message2 = 'Hello from Matt'
[0.001s] playground.py:18 (set) config = {'debug': True, 'port': 8080}
[0.001s] playground.py:19 (set) config.port = 9090
[0.001s] playground.py:20 (set) config.debug = False

Educational Mode!

Educational mode is designed to make algorithms read like a story instead of a trace. :)

Instead of raw internal logs, it shows:

• clean function calls
• meaningful variable changes
• human-readable operations
• minimal noise

Enable it with:

from logeye import log, set_mode

# Globally
set_mode("edu")


# Locally
@log(mode="edu")
def my_function():
	...

Before vs After

Default mode

[0.000s] (call) factorial = {'args': (5,), 'kwargs': {}}
[0.000s] (set) factorial.n = 5
[0.000s] (set) factorial.result = 1
[0.000s] (set) factorial.i = 1
[0.000s] (set) factorial.result = 2
...
[0.001s] (return) factorial = 120

---

Educational mode

[0.000s] Calling factorial(5)
[0.000s] n = 5
[0.000s] Calling factorial#2(4)
[0.000s] n = 4
[0.000s] Calling factorial#3(3)
[0.000s] n = 3
[0.000s] Calling factorial#4(2)
[0.000s] n = 2
[0.000s] Calling factorial#5(1)
[0.000s] n = 1
[0.000s] factorial#5(1) returned 1
[0.000s] factorial#4(2) returned 2
[0.000s] factorial#3(3) returned 6
[0.000s] factorial#2(4) returned 24
[0.001s] factorial(5) returned 120

What changes in educational mode

• Function calls become readable:

  Calling foo(1, b=2)
  

• No raw args/kwargs dictionaries

• Internal noise is removed:

  • no <func ...>
  • no test/module prefixes
  • no irrelevant internals

• Data structure operations are human-friendly:

  Added 5 to arr -> [1, 2, 5]
  

Example - Educational Factorial

from logeye import log, l

l("FACTORIAL")


@log(mode="edu")
def factorial(n):
	if n == 1:
		return 1
	return n * factorial(n - 1)


factorial(5)

Output:

[0.000s] FACTORIAL
[0.000s] Calling factorial(5)
[0.000s] Calling factorial(4)
[0.000s] Calling factorial(3)
[0.000s] Calling factorial(2)
[0.000s] Calling factorial(1)
[0.000s] Returned 1
[0.000s] Returned 2
[0.000s] Returned 6
[0.000s] Returned 24
[0.000s] Returned 120

It’s especially useful for:

• learning recursion
• understanding sorting algorithms
• teaching data structures
• quickly verifying logic without a debugger

Logging functions

Decorate a function or wrap it with log:

from logeye import log


@log
def add(a, b):
	total = a + b
	return total


add(2, 3)

[0.001s] demo9.py:17 (call) add = {'args': (2, 3), 'kwargs': {}}
[0.001s] demo9.py:13 (set) add.a = 2
[0.001s] demo9.py:13 (set) add.b = 3
[0.001s] demo9.py:14 (set) add.total = 5
[0.001s] demo9.py:14 (return) add = 5

This will log:

• the function call
• local variable changes inside the function
• the return value

Advanced function logging

You can customise how functions are logged using @log(...):

Control verbosity

from logeye import log


@log(level="call")
def foo():
	x = 10
	return x

Levels:

• "call" - only function calls and returns
• "state" - variable changes only (no call spam)
• "full" - full tracing (default)

from logeye import log


@log(filter=["x"])
def foo():
	x = 10
	y = 20
	return x + y

Only selected variables will be logged.

from logeye import log


@log(filepath="logs/my_func.log")
def foo():
	x = 10
	return x

Logs for this function will be written to a file instead of stdout.

Combos

from logeye import log


@log(level="state", filter=["queue"], filepath="queue.log")
def process():
	queue = []
	queue.append(1)
	queue.append(2)

Logging objects

log() can wrap mappings and objects with __dict__ into a LoggedObject:

from logeye import log

settings = log({"theme": "dark", "volume": 3})
settings.theme = "light"
settings.volume += 1

You can also pass an object:

from logeye import *


@log
class User:
	def __init__(self):
		self.name = "Matt"
		self.active = True


user = l(User())
user.name = "For"

[0.001s] demo8.py:11 (call) User.__init__ = {'args': (<__main__.User object at 0x7fbacb1f0980>,), 'kwargs': {}}
[0.001s] demo8.py:7 (set) user.name = 'Matt'
[0.001s] demo8.py:8 (set) user.active = True
[0.001s] demo8.py:11 (set) user = {}
[0.001s] demo8.py:12 (set) user.name = 'For'

Messages

Use log() with a string to emit a formatted message:

from logeye import log

name = "Matt"
email = "mattfor@relaxy.xyz"
log("Current user: $name\nEmail: $email")

# Also works like this!
log("Current user: {}\nEmail: {}", "Matt", "mattfor@relaxy.xyz")

[0.001s] demo9.py:5 
Current user: Matt
Email: mattfor@relaxy.xyz
[0.002s] demo9.py:7 
Current user: Matt
Email: mattfor@relaxy.xyz

str.format() is tried first. If that fails, the logger also tries caller globals / locals and template substitution.

Utility functions

watch(value, name=None)

Wraps a value for logging without changing its type unless needed.

toggle_logs(True/False)

Disable or enable logging globally.

set_path_mode(mode)

Controls how file paths are shown in output.

Accepted values:

• absolute
• project
• file

set_output_formatter(func)

Replace the default formatter.

Signature:

func(elapsed, kind, name, value, filename, lineno)

reset_output_formatter()

Restore the built-in formatter.

Output format

By default, messages look like this:
(note, the path by default is relative to the run directory of the file you're launching the module in)

[0.123s] path/to/file.py:42 (set) x = 10

For plain messages:

[0.123s] path/to/file.py:42 some text

File logging

from logeye.config import set_global_log_file, toggle_global_log_file

set_global_log_file("logs/app.log")
toggle_global_log_file(True)

All logs will now be written to the specified file. To disable: toggle_global_log_file(False)

Some Usage Examples

Example 1: Factorial

Code

from logeye import log, l

l("FACTORIAL - BY ITERATION")


# Iteration
@log
def factorial(n):
	result = 1
	for i in range(1, n + 1):
		result *= i
	return result


factorial(5)

l("FACTORIAL - BY RECURSION")


# Recursion
@log
def factorial(n):
	if n == 1:
		return 1
	return n * factorial(n - 1)


factorial(5)

Output

[0.002s] demo_factorial.py:3 FACTORIAL - BY ITERATION
[0.002s] demo_factorial.py:15 (call) factorial = {'args': (5,), 'kwargs': {}}
[0.002s] demo_factorial.py:9 (set) factorial.n = 5
[0.002s] demo_factorial.py:10 (set) factorial.result = 1
[0.002s] demo_factorial.py:11 (set) factorial.i = 1
[0.002s] demo_factorial.py:11 (set) factorial.i = 2
[0.002s] demo_factorial.py:10 (set) factorial.result = 2
[0.002s] demo_factorial.py:11 (set) factorial.i = 3
[0.002s] demo_factorial.py:10 (set) factorial.result = 6
[0.002s] demo_factorial.py:11 (set) factorial.i = 4
[0.002s] demo_factorial.py:10 (set) factorial.result = 24
[0.002s] demo_factorial.py:11 (set) factorial.i = 5
[0.002s] demo_factorial.py:10 (set) factorial.result = 120
[0.002s] demo_factorial.py:12 (return) factorial = 120
[0.002s] demo_factorial.py:17 FACTORIAL - BY RECURRENCY
[0.002s] demo_factorial.py:28 (call) factorial = {'args': (5,), 'kwargs': {}}
[0.002s] demo_factorial.py:23 (set) factorial.n = 5
[0.002s] demo_factorial.py:25 (call) factorial_2 = {'args': (4,), 'kwargs': {}}
[0.002s] demo_factorial.py:23 (set) factorial_2.n = 4
[0.002s] demo_factorial.py:25 (call) factorial_3 = {'args': (3,), 'kwargs': {}}
[0.002s] demo_factorial.py:23 (set) factorial_3.n = 3
[0.002s] demo_factorial.py:25 (call) factorial_4 = {'args': (2,), 'kwargs': {}}
[0.002s] demo_factorial.py:23 (set) factorial_4.n = 2
[0.002s] demo_factorial.py:25 (call) factorial_5 = {'args': (1,), 'kwargs': {}}
[0.002s] demo_factorial.py:23 (set) factorial_5.n = 1
[0.002s] demo_factorial.py:24 (return) factorial_5 = 1
[0.002s] demo_factorial.py:25 (return) factorial_4 = 2
[0.002s] demo_factorial.py:25 (return) factorial_3 = 6
[0.002s] demo_factorial.py:25 (return) factorial_2 = 24
[0.002s] demo_factorial.py:25 (return) factorial = 120

Example 2: Dijkstra

from logeye import log, l

l("DIJKSTRA - SHORTEST PATH")


@log
def dijkstra(graph, start):
	distances = {node: float("inf") for node in graph}
	distances[start] = 0

	visited = set()
	queue = [(0, start)]

	while queue:
		current_dist, node = queue.pop(0)

		if node in visited:
			continue

		visited.add(node)

		for neighbor, weight in graph[node].items():
			new_dist = current_dist + weight

			if new_dist < distances[neighbor]:
				distances[neighbor] = new_dist
				queue.append((new_dist, neighbor))

		queue.sort()

	return distances


graph = {
	"A": {"B": 1, "C": 4},
	"B": {"C": 2, "D": 5},
	"C": {"D": 1},
	"D": {}
}

dijkstra(graph, "A")

Output

[0.000s] demo_dijkstra.py:3 DIJKSTRA - SHORTEST PATH
[0.000s] demo_dijkstra.py:41 (call) dijkstra = {'args': ({'A': {'B': 1, 'C': 4}, 'B': {'C': 2, 'D': 5}, 'C': {'D': 1}, 'D': {}}, 'A'), 'kwargs': {}}
[0.000s] demo_dijkstra.py:8 (set) dijkstra.graph = {'A': {'B': 1, 'C': 4}, 'B': {'C': 2, 'D': 5}, 'C': {'D': 1}, 'D': {}}
[0.000s] demo_dijkstra.py:8 (set) dijkstra.start = 'A'
[0.000s] demo_dijkstra.py:8 (set) dijkstra.node = 'A'
[0.000s] demo_dijkstra.py:8 (set) dijkstra.node = 'B'
[0.000s] demo_dijkstra.py:8 (set) dijkstra.node = 'C'
[0.000s] demo_dijkstra.py:8 (set) dijkstra.node = 'D'
[0.000s] demo_dijkstra.py:9 (set) dijkstra.distances = {'A': inf, 'B': inf, 'C': inf, 'D': inf}
[0.000s] demo_dijkstra.py:9 (change) dijkstra.distances.A = {'op': 'setitem', 'value': 0, 'state': {'A': 0, 'B': inf, 'C': inf, 'D': inf}}
[0.000s] demo_dijkstra.py:12 (set) dijkstra.visited = set()
[0.000s] demo_dijkstra.py:14 (set) dijkstra.queue = [(0, 'A')]
[0.001s] demo_dijkstra.py:15 (change) dijkstra.queue = {'op': 'pop', 'index': 0, 'value': (0, 'A'), 'state': []}
[0.001s] demo_dijkstra.py:17 (set) dijkstra.node = 'A'
[0.001s] demo_dijkstra.py:17 (set) dijkstra.current_dist = 0
[0.001s] demo_dijkstra.py:20 (change) dijkstra.visited = {'op': 'add', 'value': 'A', 'state': {'A'}}
[0.001s] demo_dijkstra.py:23 (set) dijkstra.neighbor = 'B'
[0.001s] demo_dijkstra.py:23 (set) dijkstra.weight = 1
[0.001s] demo_dijkstra.py:25 (set) dijkstra.new_dist = 1
[0.001s] demo_dijkstra.py:26 (change) dijkstra.distances.B = {'op': 'setitem', 'value': 1, 'state': {'A': 0, 'B': 1, 'C': inf, 'D': inf}}
[0.001s] demo_dijkstra.py:27 (change) dijkstra.queue = {'op': 'append', 'value': (1, 'B'), 'state': [(1, 'B')]}
[0.001s] demo_dijkstra.py:23 (set) dijkstra.neighbor = 'C'
[0.001s] demo_dijkstra.py:23 (set) dijkstra.weight = 4
[0.001s] demo_dijkstra.py:25 (set) dijkstra.new_dist = 4
[0.001s] demo_dijkstra.py:26 (change) dijkstra.distances.C = {'op': 'setitem', 'value': 4, 'state': {'A': 0, 'B': 1, 'C': 4, 'D': inf}}
[0.001s] demo_dijkstra.py:27 (change) dijkstra.queue = {'op': 'append', 'value': (4, 'C'), 'state': [(1, 'B'), (4, 'C')]}
[0.001s] demo_dijkstra.py:29 (change) dijkstra.queue = {'op': 'sort', 'args': (), 'kwargs': {}, 'state': [(1, 'B'), (4, 'C')]}
[0.001s] demo_dijkstra.py:15 (change) dijkstra.queue = {'op': 'pop', 'index': 0, 'value': (1, 'B'), 'state': [(4, 'C')]}
[0.001s] demo_dijkstra.py:17 (set) dijkstra.node = 'B'
[0.001s] demo_dijkstra.py:17 (set) dijkstra.current_dist = 1
[0.001s] demo_dijkstra.py:20 (change) dijkstra.visited = {'op': 'add', 'value': 'B', 'state': {'A', 'B'}}
[0.001s] demo_dijkstra.py:23 (set) dijkstra.weight = 2
[0.001s] demo_dijkstra.py:25 (set) dijkstra.new_dist = 3
[0.002s] demo_dijkstra.py:26 (change) dijkstra.distances.C = {'op': 'setitem', 'value': 3, 'state': {'A': 0, 'B': 1, 'C': 3, 'D': inf}}
[0.002s] demo_dijkstra.py:27 (change) dijkstra.queue = {'op': 'append', 'value': (3, 'C'), 'state': [(4, 'C'), (3, 'C')]}
[0.002s] demo_dijkstra.py:23 (set) dijkstra.neighbor = 'D'
[0.002s] demo_dijkstra.py:23 (set) dijkstra.weight = 5
[0.002s] demo_dijkstra.py:25 (set) dijkstra.new_dist = 6
[0.002s] demo_dijkstra.py:26 (change) dijkstra.distances.D = {'op': 'setitem', 'value': 6, 'state': {'A': 0, 'B': 1, 'C': 3, 'D': 6}}
[0.002s] demo_dijkstra.py:27 (change) dijkstra.queue = {'op': 'append', 'value': (6, 'D'), 'state': [(4, 'C'), (3, 'C'), (6, 'D')]}
[0.002s] demo_dijkstra.py:29 (change) dijkstra.queue = {'op': 'sort', 'args': (), 'kwargs': {}, 'state': [(3, 'C'), (4, 'C'), (6, 'D')]}
[0.002s] demo_dijkstra.py:15 (change) dijkstra.queue = {'op': 'pop', 'index': 0, 'value': (3, 'C'), 'state': [(4, 'C'), (6, 'D')]}
[0.002s] demo_dijkstra.py:17 (set) dijkstra.node = 'C'
[0.002s] demo_dijkstra.py:17 (set) dijkstra.current_dist = 3
[0.002s] demo_dijkstra.py:20 (change) dijkstra.visited = {'op': 'add', 'value': 'C', 'state': {'C', 'A', 'B'}}
[0.002s] demo_dijkstra.py:23 (set) dijkstra.weight = 1
[0.002s] demo_dijkstra.py:25 (set) dijkstra.new_dist = 4
[0.002s] demo_dijkstra.py:26 (change) dijkstra.distances.D = {'op': 'setitem', 'value': 4, 'state': {'A': 0, 'B': 1, 'C': 3, 'D': 4}}
[0.003s] demo_dijkstra.py:27 (change) dijkstra.queue = {'op': 'append', 'value': (4, 'D'), 'state': [(4, 'C'), (6, 'D'), (4, 'D')]}
[0.003s] demo_dijkstra.py:29 (change) dijkstra.queue = {'op': 'sort', 'args': (), 'kwargs': {}, 'state': [(4, 'C'), (4, 'D'), (6, 'D')]}
[0.003s] demo_dijkstra.py:15 (change) dijkstra.queue = {'op': 'pop', 'index': 0, 'value': (4, 'C'), 'state': [(4, 'D'), (6, 'D')]}
[0.003s] demo_dijkstra.py:17 (set) dijkstra.current_dist = 4
[0.003s] demo_dijkstra.py:15 (change) dijkstra.queue = {'op': 'pop', 'index': 0, 'value': (4, 'D'), 'state': [(6, 'D')]}
[0.003s] demo_dijkstra.py:17 (set) dijkstra.node = 'D'
[0.003s] demo_dijkstra.py:20 (change) dijkstra.visited = {'op': 'add', 'value': 'D', 'state': {'C', 'A', 'D', 'B'}}
[0.003s] demo_dijkstra.py:29 (change) dijkstra.queue = {'op': 'sort', 'args': (), 'kwargs': {}, 'state': [(6, 'D')]}
[0.003s] demo_dijkstra.py:15 (change) dijkstra.queue = {'op': 'pop', 'index': 0, 'value': (6, 'D'), 'state': []}
[0.003s] demo_dijkstra.py:17 (set) dijkstra.current_dist = 6
[0.003s] demo_dijkstra.py:31 (return) dijkstra = {'A': 0, 'B': 1, 'C': 3, 'D': 4}

Inspiration

Idea came to be during Warsaw IT Days 2026. During the Python lecture "Logging module adventures".
I thought there definitely was an easier way to do it without repeating yourself constantly, and it turns out there was!

Limitations

• variable name inference is best-effort and may fail in complex or highly dynamic expressions
• some edge cases (e.g. deeply nested calls, chained expressions, unusual syntax) may fall back to a generic name like "set"
• lambda functions are not automatically traced unless explicitly wrapped with log()
• function tracing relies on sys.settrace() and may introduce overhead in performance-sensitive code
• logging inside heavily recursive or multithreaded code may produce noisy or hard-to-follow output
• AST-based analysis requires access to source files and may not work correctly in environments without source code ( e.g. compiled/obfuscated code, some REPLs)
• tuple assignment tracking depends on call order and may behave unexpectedly in complex expressions
• object wrapping only supports mappings and objects with __dict__
• custom objects with unusual attribute behaviour may not be fully tracked
• logging output is intended for debugging and introspection, not structured logging or production telemetry
• local variables may be wrapped at runtime to enable mutation tracking, which can affect identity checks and edge-case behaviour

Contact

If you have questions, ideas, or run into issues:

• please open an issue!
• or email me mattfor@relaxy.xyz
• or add me on discord @mattfor

License

MIT License © 2026

See LICENSE for details.

Version 1.4.0