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diff --git a/share/extensions/inkex/units.py b/share/extensions/inkex/units.py
new file mode 100644
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+++ b/share/extensions/inkex/units.py
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+# -*- coding: utf-8 -*-
+#
+# Copyright (c) Aaron Spike <aaron@ekips.org>
+#               Aurélio A. Heckert <aurium(a)gmail.com>
+#               Bulia Byak <buliabyak@users.sf.net>
+#               Nicolas Dufour, nicoduf@yahoo.fr
+#               Peter J. R. Moulder <pjrm@users.sourceforge.net>
+#               Martin Owens <doctormo@gmail.com>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+"""
+Convert to and from various units and find the closest matching unit.
+"""
+
+import re
+
+# a dictionary of unit to user unit conversion factors
+CONVERSIONS = {
+    "in": 96.0,
+    "pt": 1.3333333333333333,
+    "px": 1.0,
+    "mm": 3.779527559055118,
+    "cm": 37.79527559055118,
+    "m": 3779.527559055118,
+    "km": 3779527.559055118,
+    "Q": 0.94488188976378,
+    "pc": 16.0,
+    "yd": 3456.0,
+    "ft": 1152.0,
+    "": 1.0,  # Default px
+}
+
+# allowed unit types, including percentages, relative units, and others
+# that are not suitable for direct conversion to a length.
+# Note that this is _not_ an exhaustive list of allowed unit types.
+UNITS = [
+    "in",
+    "pt",
+    "px",
+    "mm",
+    "cm",
+    "m",
+    "km",
+    "Q",
+    "pc",
+    "yd",
+    "ft",
+    "",
+    "%",
+    "em",
+    "ex",
+    "ch",
+    "rem",
+    "vw",
+    "vh",
+    "vmin",
+    "vmax",
+    "deg",
+    "grad",
+    "rad",
+    "turn",
+    "s",
+    "ms",
+    "Hz",
+    "kHz",
+    "dpi",
+    "dpcm",
+    "dppx",
+]
+
+UNIT_MATCH = re.compile(rf"({'|'.join(UNITS)})")
+NUMBER_MATCH = re.compile(r"(([-+]?[0-9]+(\.[0-9]*)?|[-+]?\.[0-9]+)([eE][-+]?[0-9]+)?)")
+BOTH_MATCH = re.compile(rf"^\s*{NUMBER_MATCH.pattern}\s*{UNIT_MATCH.pattern}\s*$")
+
+
+def parse_unit(value, default_unit="px", default_value=None):
+    """
+    Takes a value such as 55.32px and returns (55.32, 'px')
+    Returns default (None) if no match can be found
+    """
+    ret = BOTH_MATCH.match(str(value))
+    if ret:
+        return float(ret.groups()[0]), ret.groups()[-1] or default_unit
+    return (default_value, default_unit) if default_value is not None else None
+
+
+def are_near_relative(point_a, point_b, eps=0.01):
+    """Return true if the points are near to eps"""
+    return (point_a - point_b <= point_a * eps) and (
+        point_a - point_b >= -point_a * eps
+    )
+
+
+def discover_unit(value, viewbox, default="px"):
+    """Attempt to detect the unit being used based on the viewbox"""
+    # Default 100px when width can't be parsed
+    (value, unit) = parse_unit(value, default_value=100.0)
+    if unit not in CONVERSIONS:
+        return default
+    this_factor = CONVERSIONS[unit] * value / viewbox
+
+    # try to find the svgunitfactor in the list of units known. If we don't find
+    # something, ...
+    for unit, unit_factor in CONVERSIONS.items():
+        if unit != "":
+            # allow 1% error in factor
+            if are_near_relative(this_factor, unit_factor, eps=0.01):
+                return unit
+    return default
+
+
+def convert_unit(value, to_unit, default="px"):
+    """Returns userunits given a string representation of units in another system
+
+    Args:
+        value: <length> string
+        to_unit: unit to convert to
+        default: if ``value`` contains no unit, what unit should be assumed.
+
+            .. versionadded:: 1.1
+    """
+    value, from_unit = parse_unit(value, default_unit=default, default_value=0.0)
+    if from_unit in CONVERSIONS and to_unit in CONVERSIONS:
+        return (
+            value * CONVERSIONS[from_unit] / CONVERSIONS.get(to_unit, CONVERSIONS["px"])
+        )
+    return 0.0
+
+
+def render_unit(value, unit):
+    """Checks and then renders a number with its unit"""
+    try:
+        if isinstance(value, str):
+            (value, unit) = parse_unit(value, default_unit=unit)
+        return f"{value:.6g}{ unit:s}"
+    except TypeError:
+        return ""