xmllens

Deep structural comparison for XML documents with per-path numeric tolerance and XPath-like targeting.

Overview

xmllens is a lightweight Python library for comparing two XML documents with fine-grained tolerance control.

It supports:

• ✅ Global absolute (abs_tol) and relative (rel_tol) numeric tolerances
• ✅ Per-path tolerance overrides via XPath-like expressions
• ✅ Ignoring volatile or irrelevant XML elements
• ✅ Detailed debug logs that explain why two XMLs differ

It’s ideal for comparing configuration files, XML-based API payloads, or serialized data models where small numeric drifts are expected.

Installation

pip install xmllens

Supported Path Patterns

xmllens implements a simplified subset of XPath syntax:

Pattern	Description
/a/b/c	Exact element path
/items/item[1]/price	Specific index
/items/*/price	Any element name
//price	Recursive descent
/root/*	Wildcard for any child element

Full API

compare_xml(
    xml_a: str,
    xml_b: str,
    *,
    ignore_fields: list[str] = None,
    abs_tol: float = 0.0,
    rel_tol: float = 0.0,
    abs_tol_fields: dict[str, float] = None,
    rel_tol_fields: dict[str, float] = None,
    epsilon: float = 1e-12,
    show_debug: bool = False,
) -> bool

Parameter	Description
xml_a, xml_b	XML documents as strings
ignore_fields	XPath-like patterns to skip during comparison
abs_tol	Global absolute numeric tolerance
rel_tol	Global relative numeric tolerance
abs_tol_fields	Per-path absolute tolerances
rel_tol_fields	Per-path relative tolerances
epsilon	Small float to absorb FP rounding errors
show_debug	Enable detailed comparison logs

Examples

from xmllens import compare_xml

xml1 = "<sensor><temp>21.5</temp><humidity>48.0</humidity></sensor>"
xml2 = "<sensor><temp>21.7</temp><humidity>48.5</humidity></sensor>"

# Default tolerances
res = compare_xml(xml1, xml2, abs_tol=0.05, rel_tol=0.01, show_debug=True)
print(res)  # False

### Output (debug)

[NUMERIC COMPARE] /sensor/temp: 21.5 vs 21.7 | diff=0.200000 | abs_tol=0.05 | rel_tol=0.01 | threshold=0.217000
[MATCH NUMERIC] /sensor/temp: within tolerance
[NUMERIC COMPARE] /sensor/humidity: 48.0 vs 48.5 | diff=0.500000 | abs_tol=0.05 | rel_tol=0.01 | threshold=0.485000
[FAIL NUMERIC] /sensor/humidity → diff=0.500000 > threshold=0.485000
[FAIL IN ELEMENT] /sensor/humidity

Simple Value Mismatch

xml1 = "<root><x>1</x></root>"
xml2 = "<root><x>2</x></root>"

result = compare_xml(xml1, xml2)
print(result)  # False

Tag Mismatch

xml1 = "<root><x>1</x></root>"
xml2 = "<root><y>1</y></root>"

result = compare_xml(xml1, xml2)
print(result)  # False

Global Tolerances

Absolute Tolerance

xml1 = "<sensor><temp>20.0</temp></sensor>"
xml2 = "<sensor><temp>20.05</temp></sensor>"

result = compare_xml(xml1, xml2, abs_tol=0.1)
print(result)  # True

Relative Tolerance

xml1 = "<sensor><humidity>100.0</humidity></sensor>"
xml2 = "<sensor><humidity>104.0</humidity></sensor>"

result = compare_xml(xml1, xml2, rel_tol=0.05)
print(result)  # True  (5% tolerance)

Per-Path Tolerances

Per-Path Absolute Tolerance

xml1 = "<root><a>1.0</a><b>2.0</b></root>"
xml2 = "<root><a>1.5</a><b>2.9</b></root>"

abs_tol_fields = {"/root/b": 1.0}

result = compare_xml(xml1, xml2, abs_tol=0.5, abs_tol_fields=abs_tol_fields)
print(result)  # True

Per-Path Relative Tolerance

xml1 = "<values><x>100</x><y>200</y></values>"
xml2 = "<values><x>110</x><y>210</y></values>"

rel_tol_fields = {"/values/x": 0.2}  # 20%

result = compare_xml(xml1, xml2, rel_tol=0.05, rel_tol_fields=rel_tol_fields)
print(result)  # True

Ignoring fields

Simple Ignore Path

xml1 = "<root><id>1</id><timestamp>now</timestamp></root>"
xml2 = "<root><id>1</id><timestamp>later</timestamp></root>"

ignore_fields = ["/root/timestamp"]

result = compare_xml(xml1, xml2, ignore_fields=ignore_fields)
print(result)  # True

More Examples

Ignore multiple fields with different patterns:

• Exact path: /user/profile/updated_at

• Wildcard: /devices/*/debug

• Recursive: //trace

xml1 = """
<data>
    <user>
        <id>7</id>
        <profile><updated_at>2025-10-14T10:00:00Z</updated_at><age>30</age></profile>
    </user>
    <devices>
        <device><id>d1</id><debug>alpha</debug><temp>20.0</temp></device>
        <device><id>d2</id><debug>beta</debug><temp>20.1</temp></device>
    </devices>
    <sessions>
        <session><events><event><meta><trace>abc</trace></meta><value>10.0</value></event></events></session>
        <session><events><event><meta><trace>def</trace></meta><value>10.5</value></event></events></session>
    </sessions>
</data>
"""

xml2 = """
<data>
    <user>
        <id>7</id>
        <profile><updated_at>2025-10-15T10:00:05Z</updated_at><age>30</age></profile>
    </user>
    <devices>
        <device><id>d1</id><debug>changed</debug><temp>20.05</temp></device>
        <device><id>d2</id><debug>changed</debug><temp>20.18</temp></device>
    </devices>
    <sessions>
        <session><events><event><meta><trace>xyz</trace></meta><value>10.01</value></event></events></session>
        <session><events><event><meta><trace>uvw</trace></meta><value>10.52</value></event></events></session>
    </sessions>
</data>
"""

ignore_fields = [
    "/data/user/profile/updated_at",
    "/data/devices/*/debug",
    "//trace",
]

result = compare_xml(
    xml1, xml2,
    ignore_fields=ignore_fields,
    abs_tol=0.05,
    rel_tol=0.02
)
print(result)  # True

combining absolute and relative tolerances for different fields.

xml1 = """
<station>
    <id>ST-42</id>
    <location>Paris</location>
    <version>1.0</version>
    <metrics>
        <temperature>21.5</temperature>
        <humidity>48.0</humidity>
        <pressure>1013.2</pressure>
        <wind_speed>5.4</wind_speed>
    </metrics>
    <status><battery_level>96.0</battery_level></status>
</station>
"""

xml2 = """
<station>
    <id>ST-42</id>
    <location>Paris</location>
    <version>1.03</version>
    <metrics>
        <temperature>21.6</temperature>
        <humidity>49.3</humidity>
        <pressure>1013.5</pressure>
        <wind_speed>5.6</wind_speed>
    </metrics>
    <status><battery_level>94.8</battery_level></status>
</station>
"""

abs_tol_fields = {
    "/station/version": 0.1,
    "/station/metrics/humidity": 2.0,
    "/station/status/battery_level": 2.0,
}

rel_tol_fields = {
    "/station/metrics/wind_speed": 0.05,
}

result = compare_xml(
    xml1, xml2,
    abs_tol=0.05,
    rel_tol=0.01,
    abs_tol_fields=abs_tol_fields,
    rel_tol_fields=rel_tol_fields
)
print(result)  # True

Tips

• Elements are compared in order.

• Attributes are compared strictly.

• Whitespace is trimmed before comparison.

• To ignore volatile elements (timestamps, UUIDs, etc.), use ignore_fields.

License

Apache License 2.0 — © 2025 Mohamed Tahri Contributions welcome 🤝