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<h1>Source code for astropy.constants.constant</h1><div class="highlight"><pre>
<span class="c"># Licensed under a 3-clause BSD style license - see LICENSE.rst</span>
<span class="kn">import</span> <span class="nn">functools</span>
<span class="kn">import</span> <span class="nn">types</span>
<span class="kn">import</span> <span class="nn">warnings</span>
<span class="kn">from</span> <span class="nn">..units.core</span> <span class="kn">import</span> <span class="n">Unit</span><span class="p">,</span> <span class="n">UnitsException</span>
<span class="kn">from</span> <span class="nn">..units.quantity</span> <span class="kn">import</span> <span class="n">Quantity</span>
<span class="kn">from</span> <span class="nn">..utils</span> <span class="kn">import</span> <span class="n">lazyproperty</span>
<span class="n">__all__</span> <span class="o">=</span> <span class="p">[</span><span class="s">'Constant'</span><span class="p">,</span> <span class="s">'EMConstant'</span><span class="p">]</span>
<span class="k">class</span> <span class="nc">ConstantMeta</span><span class="p">(</span><span class="nb">type</span><span class="p">):</span>
<span class="sd">"""Metaclass for the :class:`Constant`. The primary purpose of this is to</span>
<span class="sd"> wrap the double-underscore methods of :class:`Quantity` which is the</span>
<span class="sd"> superclass of :class:`Constant`.</span>
<span class="sd"> In particular this wraps the operator overloads such as `__add__` to</span>
<span class="sd"> prevent their use with constants such as ``e`` from being used in</span>
<span class="sd"> expressions without specifying a system. The wrapper checks to see if the</span>
<span class="sd"> constant is listed (by name) in ``Constant._has_incompatible_units``, a set</span>
<span class="sd"> of those constants that are defined in different systems of units are</span>
<span class="sd"> physically incompatible. It also performs this check on each `Constant` if</span>
<span class="sd"> it hasn't already been performed (the check is deferred until the</span>
<span class="sd"> `Constant` is actually used in an expression to speed up import times,</span>
<span class="sd"> among other reasons).</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="nf">__new__</span><span class="p">(</span><span class="n">mcls</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">bases</span><span class="p">,</span> <span class="n">d</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">wrap</span><span class="p">(</span><span class="n">meth</span><span class="p">):</span>
<span class="nd">@functools.wraps</span><span class="p">(</span><span class="n">meth</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">wrapper</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="n">name_lower</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">name</span><span class="o">.</span><span class="n">lower</span><span class="p">()</span>
<span class="n">instances</span> <span class="o">=</span> <span class="n">Constant</span><span class="o">.</span><span class="n">_registry</span><span class="p">[</span><span class="n">name_lower</span><span class="p">]</span>
<span class="k">if</span> <span class="ow">not</span> <span class="bp">self</span><span class="o">.</span><span class="n">_checked_units</span><span class="p">:</span>
<span class="k">for</span> <span class="n">inst</span> <span class="ow">in</span> <span class="n">instances</span><span class="o">.</span><span class="n">values</span><span class="p">():</span>
<span class="k">try</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">unit</span><span class="o">.</span><span class="n">to</span><span class="p">(</span><span class="n">inst</span><span class="o">.</span><span class="n">unit</span><span class="p">)</span>
<span class="k">except</span> <span class="n">UnitsException</span><span class="p">:</span>
<span class="n">Constant</span><span class="o">.</span><span class="n">_has_incompatible_units</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">name_lower</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_checked_units</span> <span class="o">=</span> <span class="bp">True</span>
<span class="k">if</span> <span class="p">(</span><span class="ow">not</span> <span class="bp">self</span><span class="o">.</span><span class="n">system</span> <span class="ow">and</span>
<span class="n">name_lower</span> <span class="ow">in</span> <span class="n">Constant</span><span class="o">.</span><span class="n">_has_incompatible_units</span><span class="p">):</span>
<span class="n">systems</span> <span class="o">=</span> <span class="nb">sorted</span><span class="p">(</span><span class="nb">filter</span><span class="p">(</span><span class="bp">None</span><span class="p">,</span> <span class="n">instances</span><span class="p">))</span>
<span class="k">raise</span> <span class="ne">TypeError</span><span class="p">(</span>
<span class="s">'Constant {0!r} does not have physically compatible '</span>
<span class="s">'units across all systems of units and cannot be '</span>
<span class="s">'combined with other values without specifying a '</span>
<span class="s">'system (eg. {1}.{2})'</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">abbrev</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">abbrev</span><span class="p">,</span>
<span class="n">systems</span><span class="p">[</span><span class="mi">0</span><span class="p">]))</span>
<span class="k">return</span> <span class="n">meth</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span>
<span class="k">return</span> <span class="n">wrapper</span>
<span class="c"># The wrapper applies to so many of the __ methods that it's easier to</span>
<span class="c"># just exclude the ones it doesn't apply to</span>
<span class="n">exclude</span> <span class="o">=</span> <span class="nb">set</span><span class="p">([</span><span class="s">'__init__'</span><span class="p">,</span> <span class="s">'__str__'</span><span class="p">,</span> <span class="s">'__repr__'</span><span class="p">])</span>
<span class="k">for</span> <span class="n">attr</span><span class="p">,</span> <span class="n">value</span> <span class="ow">in</span> <span class="nb">vars</span><span class="p">(</span><span class="n">Quantity</span><span class="p">)</span><span class="o">.</span><span class="n">items</span><span class="p">():</span>
<span class="k">if</span> <span class="p">(</span><span class="nb">isinstance</span><span class="p">(</span><span class="n">value</span><span class="p">,</span> <span class="n">types</span><span class="o">.</span><span class="n">FunctionType</span><span class="p">)</span> <span class="ow">and</span>
<span class="n">attr</span><span class="o">.</span><span class="n">startswith</span><span class="p">(</span><span class="s">'__'</span><span class="p">)</span> <span class="ow">and</span> <span class="n">attr</span><span class="o">.</span><span class="n">endswith</span><span class="p">(</span><span class="s">'__'</span><span class="p">)</span> <span class="ow">and</span>
<span class="n">attr</span> <span class="ow">not</span> <span class="ow">in</span> <span class="n">exclude</span><span class="p">):</span>
<span class="n">d</span><span class="p">[</span><span class="n">attr</span><span class="p">]</span> <span class="o">=</span> <span class="n">wrap</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
<span class="k">return</span> <span class="nb">super</span><span class="p">(</span><span class="n">ConstantMeta</span><span class="p">,</span> <span class="n">mcls</span><span class="p">)</span><span class="o">.</span><span class="n">__new__</span><span class="p">(</span><span class="n">mcls</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">bases</span><span class="p">,</span> <span class="n">d</span><span class="p">)</span>
<div class="viewcode-block" id="Constant"><a class="viewcode-back" href="../../../_generated/astropy.constants.constant.Constant.html#astropy.constants.constant.Constant">[docs]</a><span class="k">class</span> <span class="nc">Constant</span><span class="p">(</span><span class="n">Quantity</span><span class="p">):</span>
<span class="sd">"""A physical or astronomical constant.</span>
<span class="sd"> These objects are quantities that are meant to represent physical</span>
<span class="sd"> constants.</span>
<span class="sd"> """</span>
<span class="n">__metaclass__</span> <span class="o">=</span> <span class="n">ConstantMeta</span>
<span class="n">_registry</span> <span class="o">=</span> <span class="p">{}</span>
<span class="n">_has_incompatible_units</span> <span class="o">=</span> <span class="nb">set</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">__new__</span><span class="p">(</span><span class="n">cls</span><span class="p">,</span> <span class="n">abbrev</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">value</span><span class="p">,</span> <span class="n">unit</span><span class="p">,</span> <span class="n">uncertainty</span><span class="p">,</span> <span class="n">reference</span><span class="p">,</span>
<span class="n">system</span><span class="o">=</span><span class="bp">None</span><span class="p">):</span>
<span class="n">name_lower</span> <span class="o">=</span> <span class="n">name</span><span class="o">.</span><span class="n">lower</span><span class="p">()</span>
<span class="n">instances</span> <span class="o">=</span> <span class="n">Constant</span><span class="o">.</span><span class="n">_registry</span><span class="o">.</span><span class="n">setdefault</span><span class="p">(</span><span class="n">name_lower</span><span class="p">,</span> <span class="p">{})</span>
<span class="k">if</span> <span class="n">system</span> <span class="ow">in</span> <span class="n">instances</span><span class="p">:</span>
<span class="n">warnings</span><span class="o">.</span><span class="n">warn</span><span class="p">(</span><span class="s">'Constant {0!r} is already has a definition in the '</span>
<span class="s">'{1!r} system'</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">system</span><span class="p">))</span>
<span class="n">inst</span> <span class="o">=</span> <span class="nb">super</span><span class="p">(</span><span class="n">Constant</span><span class="p">,</span> <span class="n">cls</span><span class="p">)</span><span class="o">.</span><span class="n">__new__</span><span class="p">(</span><span class="n">cls</span><span class="p">)</span>
<span class="k">for</span> <span class="n">c</span> <span class="ow">in</span> <span class="n">instances</span><span class="o">.</span><span class="n">values</span><span class="p">():</span>
<span class="k">if</span> <span class="n">system</span> <span class="ow">is</span> <span class="ow">not</span> <span class="bp">None</span> <span class="ow">and</span> <span class="ow">not</span> <span class="nb">hasattr</span><span class="p">(</span><span class="n">c</span><span class="o">.</span><span class="n">__class__</span><span class="p">,</span> <span class="n">system</span><span class="p">):</span>
<span class="nb">setattr</span><span class="p">(</span><span class="n">c</span><span class="p">,</span> <span class="n">system</span><span class="p">,</span> <span class="n">inst</span><span class="p">)</span>
<span class="k">if</span> <span class="n">c</span><span class="o">.</span><span class="n">system</span> <span class="ow">is</span> <span class="ow">not</span> <span class="bp">None</span> <span class="ow">and</span> <span class="ow">not</span> <span class="nb">hasattr</span><span class="p">(</span><span class="n">inst</span><span class="o">.</span><span class="n">__class__</span><span class="p">,</span> <span class="n">c</span><span class="o">.</span><span class="n">system</span><span class="p">):</span>
<span class="nb">setattr</span><span class="p">(</span><span class="n">inst</span><span class="p">,</span> <span class="n">c</span><span class="o">.</span><span class="n">system</span><span class="p">,</span> <span class="n">c</span><span class="p">)</span>
<span class="n">instances</span><span class="p">[</span><span class="n">system</span><span class="p">]</span> <span class="o">=</span> <span class="n">inst</span>
<span class="k">return</span> <span class="n">inst</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">abbrev</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">value</span><span class="p">,</span> <span class="n">unit</span><span class="p">,</span> <span class="n">uncertainty</span><span class="p">,</span> <span class="n">reference</span><span class="p">,</span>
<span class="n">system</span><span class="o">=</span><span class="bp">None</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_abbrev</span> <span class="o">=</span> <span class="n">abbrev</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_name</span> <span class="o">=</span> <span class="n">name</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_value</span> <span class="o">=</span> <span class="n">value</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_unit</span> <span class="o">=</span> <span class="n">unit</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_uncertainty</span> <span class="o">=</span> <span class="n">uncertainty</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_reference</span> <span class="o">=</span> <span class="n">reference</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_system</span> <span class="o">=</span> <span class="n">system</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_checked_units</span> <span class="o">=</span> <span class="bp">False</span>
<span class="k">def</span> <span class="nf">__repr__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="p">(</span><span class="s">'<Constant name={0!r} value={1} error={2} units={3!r} '</span>
<span class="s">'reference={4!r}>'</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">name</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">value</span><span class="p">,</span>
<span class="bp">self</span><span class="o">.</span><span class="n">uncertainty</span><span class="p">,</span> <span class="nb">str</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">unit</span><span class="p">),</span>
<span class="bp">self</span><span class="o">.</span><span class="n">reference</span><span class="p">))</span>
<span class="k">def</span> <span class="nf">__str__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="p">(</span><span class="s">' Name = {0}</span><span class="se">\n</span><span class="s">'</span>
<span class="s">' Value = {1}</span><span class="se">\n</span><span class="s">'</span>
<span class="s">' Error = {2}</span><span class="se">\n</span><span class="s">'</span>
<span class="s">' Units = {3}</span><span class="se">\n</span><span class="s">'</span>
<span class="s">' Reference = {4}'</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">name</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">value</span><span class="p">,</span>
<span class="bp">self</span><span class="o">.</span><span class="n">uncertainty</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">unit</span><span class="p">,</span>
<span class="bp">self</span><span class="o">.</span><span class="n">reference</span><span class="p">))</span>
<span class="nd">@property</span>
<div class="viewcode-block" id="Constant.abbrev"><a class="viewcode-back" href="../../../_generated/astropy.constants.constant.Constant.html#astropy.constants.constant.Constant.abbrev">[docs]</a> <span class="k">def</span> <span class="nf">abbrev</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="sd">"""A typical ASCII text abbreviation of the constant, also generally</span>
<span class="sd"> the same as the Python variable used for this constant.</span>
<span class="sd"> """</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_abbrev</span>
</div>
<span class="nd">@property</span>
<div class="viewcode-block" id="Constant.name"><a class="viewcode-back" href="../../../_generated/astropy.constants.constant.Constant.html#astropy.constants.constant.Constant.name">[docs]</a> <span class="k">def</span> <span class="nf">name</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="sd">"""The full name of the constant."""</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_name</span>
</div>
<span class="nd">@lazyproperty</span>
<div class="viewcode-block" id="Constant.unit"><a class="viewcode-back" href="../../../_generated/astropy.constants.constant.Constant.html#astropy.constants.constant.Constant.unit">[docs]</a> <span class="k">def</span> <span class="nf">unit</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="sd">"""The unit(s) in which this constant is defined."""</span>
<span class="k">return</span> <span class="n">Unit</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_unit</span><span class="p">)</span>
</div>
<span class="nd">@property</span>
<div class="viewcode-block" id="Constant.uncertainty"><a class="viewcode-back" href="../../../_generated/astropy.constants.constant.Constant.html#astropy.constants.constant.Constant.uncertainty">[docs]</a> <span class="k">def</span> <span class="nf">uncertainty</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="sd">"""The known uncertainty in this constant's value."""</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_uncertainty</span>
</div>
<span class="nd">@property</span>
<div class="viewcode-block" id="Constant.reference"><a class="viewcode-back" href="../../../_generated/astropy.constants.constant.Constant.html#astropy.constants.constant.Constant.reference">[docs]</a> <span class="k">def</span> <span class="nf">reference</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="sd">"""The source used for the value of this constant."""</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_reference</span>
</div>
<span class="nd">@property</span>
<div class="viewcode-block" id="Constant.system"><a class="viewcode-back" href="../../../_generated/astropy.constants.constant.Constant.html#astropy.constants.constant.Constant.system">[docs]</a> <span class="k">def</span> <span class="nf">system</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="sd">"""The system of units in which this constant is defined (typically</span>
<span class="sd"> `None` so long as the constant's units can be directly converted</span>
<span class="sd"> between systems).</span>
<span class="sd"> """</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_system</span>
</div>
<span class="nd">@property</span>
<div class="viewcode-block" id="Constant.si"><a class="viewcode-back" href="../../../_generated/astropy.constants.constant.Constant.html#astropy.constants.constant.Constant.si">[docs]</a> <span class="k">def</span> <span class="nf">si</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="sd">"""If the Constant is defined in the SI system return that instance of</span>
<span class="sd"> the constant, else convert to a Quantity in the appropriate SI units.</span>
<span class="sd"> """</span>
<span class="n">instances</span> <span class="o">=</span> <span class="n">Constant</span><span class="o">.</span><span class="n">_registry</span><span class="p">[</span><span class="bp">self</span><span class="o">.</span><span class="n">name</span><span class="o">.</span><span class="n">lower</span><span class="p">()]</span>
<span class="k">return</span> <span class="n">instances</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s">'si'</span><span class="p">)</span> <span class="ow">or</span> <span class="nb">super</span><span class="p">(</span><span class="n">Constant</span><span class="p">,</span> <span class="bp">self</span><span class="p">)</span><span class="o">.</span><span class="n">si</span>
</div>
<span class="nd">@property</span>
<div class="viewcode-block" id="Constant.cgs"><a class="viewcode-back" href="../../../_generated/astropy.constants.constant.Constant.html#astropy.constants.constant.Constant.cgs">[docs]</a> <span class="k">def</span> <span class="nf">cgs</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="sd">"""If the Constant is defined in the CGS system return that instance of</span>
<span class="sd"> the constant, else convert to a Quantity in the appropriate CGS units.</span>
<span class="sd"> """</span>
<span class="n">instances</span> <span class="o">=</span> <span class="n">Constant</span><span class="o">.</span><span class="n">_registry</span><span class="p">[</span><span class="bp">self</span><span class="o">.</span><span class="n">name</span><span class="o">.</span><span class="n">lower</span><span class="p">()]</span>
<span class="k">return</span> <span class="n">instances</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s">'cgs'</span><span class="p">)</span> <span class="ow">or</span> <span class="nb">super</span><span class="p">(</span><span class="n">Constant</span><span class="p">,</span> <span class="bp">self</span><span class="p">)</span><span class="o">.</span><span class="n">cgs</span>
</div></div>
<div class="viewcode-block" id="EMConstant"><a class="viewcode-back" href="../../../_generated/astropy.constants.constant.EMConstant.html#astropy.constants.constant.EMConstant">[docs]</a><span class="k">class</span> <span class="nc">EMConstant</span><span class="p">(</span><span class="n">Constant</span><span class="p">):</span>
<span class="sd">"""An electromagnetic constant."""</span>
<span class="nd">@property</span>
<div class="viewcode-block" id="EMConstant.cgs"><a class="viewcode-back" href="../../../_generated/astropy.constants.constant.EMConstant.html#astropy.constants.constant.EMConstant.cgs">[docs]</a> <span class="k">def</span> <span class="nf">cgs</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="sd">"""Overridden for EMConstant to raise a `TypeError` emphasizing that</span>
<span class="sd"> there are multiple EM extensions to CGS.</span>
<span class="sd"> """</span>
<span class="k">raise</span> <span class="ne">TypeError</span><span class="p">(</span><span class="s">"Cannot convert EM constants to cgs because there "</span>
<span class="s">"are different systems for E.M constants within the "</span>
<span class="s">"c.g.s system (ESU, Gaussian, etc.). Instead, "</span>
<span class="s">"directly use the constant with the appropriate "</span>
<span class="s">"suffix (e.g. e.esu, e.gauss, etc.)."</span><span class="p">)</span></div></div>
</pre></div>
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