Draft: move units functions outside DraftGui.py

The functions `getDefaultUnit`, `makeFormatSpec`, `displayExternal`
are used to get the default unit schema for lengths and angles,
and display a string with a particular format.

They aren't used in `DraftGui.py`, but are used by the
viewprovider of the Dimension objects. Therefore, they are moved
into a separate module, so that they can be imported without
using the entire `DraftGui` module.

src/Mod/Draft/draftutils/units.py

@@ -0,0 +1,124 @@
+# ***************************************************************************
+# *   Copyright (c) 2009 Yorik van Havre <yorik@uncreated.net>              *
+# *   Copyright (c) 2020 Eliud Cabrera Castillo <e.cabrera-castillo@tum.de> *
+# *                                                                         *
+# *   This file is part of the FreeCAD CAx development system.              *
+# *                                                                         *
+# *   This program is free software; you can redistribute it and/or modify  *
+# *   it under the terms of the GNU Lesser General Public License (LGPL)    *
+# *   as published by the Free Software Foundation; either version 2 of     *
+# *   the License, or (at your option) any later version.                   *
+# *   for detail see the LICENCE text file.                                 *
+# *                                                                         *
+# *   FreeCAD 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 Library General Public License for more details.                  *
+# *                                                                         *
+# *   You should have received a copy of the GNU Library General Public     *
+# *   License along with FreeCAD; if not, write to the Free Software        *
+# *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  *
+# *   USA                                                                   *
+# *                                                                         *
+# ***************************************************************************
+"""Provides utility functions related to unit handling."""
+## @package units
+# \ingroup DRAFT
+# \brief Provides utility functions related to unit handling.
+
+from PySide import QtCore
+
+import FreeCAD as App
+
+
+def get_default_unit(dim):
+    """Return default Unit of Measure for a dimension.
+
+    It is based on the user preferences.
+    """
+    if dim == 'Length':
+        qty = App.Units.Quantity(1.0, App.Units.Length)
+        uom = qty.getUserPreferred()[2]
+    elif dim == 'Angle':
+        qty = App.Units.Quantity(1.0, App.Units.Angle)
+        uom = qty.getUserPreferred()[2]
+    else:
+        uom = "xx"
+    return uom
+
+
+getDefaultUnit = get_default_unit
+
+
+def make_format_spec(decimals=4, dim='Length'):
+    """Return a string format specifier with decimals for a dimension.
+
+    It is based on the user preferences.
+    """
+    if dim == 'Length':
+        fmt_spec = "%." + str(decimals) + "f " + get_default_unit('Length')
+    elif dim == 'Angle':
+        fmt_spec = "%." + str(decimals) + "f " + get_default_unit('Angle')
+    else:
+        fmt_spec = "%." + str(decimals) + "f " + "??"
+    return fmt_spec
+
+
+makeFormatSpec = make_format_spec
+
+
+def display_external(internal_value,
+                     decimals=None, dim='Length', showUnit=True, unit=None):
+    """Return a converted value for display, according to the unit schema.
+
+    Parameters
+    ----------
+    internal_value: float
+        A value that will be transformed depending on the other parameters.
+
+    decimals: float, optional
+        It defaults ot `None`, in which case, the decimals are 2.
+
+    dim: str, optional
+        It defaults to `'Length'`. It can also be `'Angle'`.
+
+    showUnit: bool, optional
+        It defaults to `True`.
+        If it is `False` it won't show the unit.
+
+    unit: str, optional
+        A unit string such as `'mm'`, `'cm'`, `'m'`, `'in'`, `'ft'`,
+        in which to express the returned value.
+    """
+    if dim == 'Length':
+        q = App.Units.Quantity(internal_value, App.Units.Length)
+        if not unit:
+            if not decimals and showUnit:
+                return q.UserString
+
+            conversion = q.getUserPreferred()[1]
+            uom = q.getUserPreferred()[2]
+        else:
+            uom = unit
+            internal_value = q.getValueAs(unit)
+            conversion = 1
+    elif dim == 'Angle':
+        return App.Units.Quantity(internal_value, App.Units.Angle).UserString
+    else:
+        conversion = 1.0
+        if not decimals:
+            decimals = 2
+        uom = "??"
+
+    if not showUnit:
+        uom = ""
+
+    decimals = abs(decimals)  # prevent negative values
+    fmt = "{0:." + str(decimals) + "f} " + uom
+    display = fmt.format(float(internal_value) / float(conversion))
+    display = display.replace(".", QtCore.QLocale().decimalPoint())
+
+    return display
+
+
+displayExternal = display_external