npguard 0.3.0

NumPy memory observability and explanation tool

npguard

npguard is a NumPy memory observability and explanation tool.

It helps developers understand why NumPy memory usage spikes by detecting temporary allocations and explaining their causes, with safe, opt-in suggestions to reduce memory pressure.

npguard focuses on explanation, not automatic optimization.

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Installation

pip install npguard

PyPI: https://pypi.org/project/npguard/

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Motivation

NumPy can silently allocate large temporary arrays during:

• chained expressions
• broadcasting
• repeated allocations inside loops
• parallel execution

For example:

b = a * 2 + a.mean(axis=0) - 1

This single line can create multiple full-sized temporary arrays, leading to sudden memory spikes that are not obvious from the code and are often poorly explained by traditional profilers.

npguard exists to answer one question:

“Why did memory spike here?”

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Features

• Watch NumPy-heavy code blocks
• Detect memory pressure and hidden temporary allocations
• Estimate temporary memory usage and array counts
• Detect repeated allocations
• Detect parallel/threaded allocation spikes
• Detect dtype promotion signals
• Explain causes in human-readable terms
• Provide safe, opt-in optimization suggestions

Multiple ergonomics

• Context manager
• Decorator API
• Silent capture API
• Programmatic signal access

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What npguard does NOT do

• Does not modify NumPy behavior
• Does not monkey-patch NumPy
• Does not automatically reuse buffers
• Does not rewrite user code
• Does not detect memory leaks
• Is not a production monitoring tool

npguard is intended for development and debugging, not runtime enforcement.

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Example Usage

1. Basic block observation

import numpy as np
import npguard as ng

with ng.memory_watcher("basic_block"):
    a = np.random.rand(10_000, 100)
    ng.register_array(a, "a")

    b = a * 2 + a.mean(axis=0) - 1
    ng.register_array(b, "b")

    c = np.ascontiguousarray(b.T)
    ng.register_array(c, "c")

ng.report()
ng.suggest()

Output:

[npguard] Memory spike detected

[npguard] Allocation Summary (cumulative)
  a           : 7.63 MB
  b           : 7.63 MB
  c           : 7.63 MB
[INFO][npguard] Memory analysis completed (peak ~23.77 MB)
[WARN][signals.repetition] Repeated allocations detected at 1 site(s)
[INFO][suggestion] Reuse preallocated buffers inside loops

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2. Silent Capture API

with ng.capture("captured_block") as obs:
    x = np.random.rand(10_000, 100)
    ng.register_array(x, "x")

    y = x * 3
    ng.register_array(y, "y")

print(obs)

Output (excerpt):

{
  'tag': 'captured_block',
  'peak_mb': 15.26,
  'signals': {
    'parallel': None,
    'dtype_promotions': [],
    'repeated': {...},
    'temporaries': {'count': 2, 'mb': 15.26}
  }
}

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3. Decorator API

@ng.watch("decorated_function", warn_threshold_mb=5)
def compute_step():
    a = np.random.rand(10_000, 100)
    ng.register_array(a, "a")
    return a * 2 + a.mean(axis=0)

compute_step()
ng.suggest()

Output:

[npguard] Memory spike detected
[INFO][npguard] Memory analysis completed (peak ~15.26 MB)
[WARN][signals.repetition] Repeated allocations detected at 1 site(s)
[INFO][suggestion] Reuse preallocated buffers inside loops

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4. profile() Helper

def pipeline():
    a = np.random.rand(10_000, 100)
    ng.register_array(a, "a")
    return np.ascontiguousarray(a.T)

ng.profile(pipeline)
ng.suggest()

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5. NEW in v0.3 — Structured Signal Access

print("Peak MB:", ng.last("peak_mb"))
print("Repeated allocations:", bool(ng.last("signals.repeated")))
print("Dtype promotions:", bool(ng.last("signals.dtype_promotions")))
print("Parallel allocations:", bool(ng.last("signals.parallel")))

Output:

Peak MB: 15.26
Repeated allocations: True
Dtype promotions: False
Parallel allocations: False

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6. NEW in v0.3 — Parallel Allocation Detection

import threading

def threaded_alloc():
    a = np.random.rand(5_000, 100)
    ng.register_array(a, "threaded")

with ng.memory_watcher("thread_test"):
    t1 = threading.Thread(target=threaded_alloc)
    t2 = threading.Thread(target=threaded_alloc)
    t1.start()
    t2.start()
    t1.join()
    t2.join()

ng.suggest()

Output:

[WARN][signals.parallel] Parallel temporary allocations detected across threads
[INFO][suggestion] Consider thread-local buffers or avoiding shared temporaries

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7. Reset State (v0.3 fix)

print("Before reset:", ng.last())
ng.reset()
print("After reset:", ng.last())

Output:

Before reset: {...}
After reset: {}

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When to Use npguard

• Debugging unexpected NumPy memory spikes
• Understanding temporary array creation
• Learning memory-aware NumPy patterns
• Investigating OOMs during pipeline scaling
• Second-pass performance and memory analysis

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Target Audience

• NumPy users working with medium to large arrays
• Developers debugging memory pressure (not leaks)
• Engineers who want explanations rather than auto-fixes

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Project Status

• Version: 0.3.0
• Status: early but stable
• API: conservative and explanation-first

Future versions may improve signal accuracy and aggregation, while preserving the non-invasive philosophy.

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License

MIT License