I am adding a layer to map docyment through and stand alone ArcPy snippet like this
MXD <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>mapping<SPAN class="punctuation token">.</SPAN>MapDocument<SPAN class="punctuation token">(</SPAN>r<SPAN class="string token">"C:\\arcgis\\ArcTutor\\AAA\\MXDs\\map.mxd"</SPAN><SPAN class="punctuation token">)</SPAN>
df <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>mapping<SPAN class="punctuation token">.</SPAN>ListDataFrames<SPAN class="punctuation token">(</SPAN>MXD<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">[</SPAN><SPAN class="number token">0</SPAN><SPAN class="punctuation token">]</SPAN>
<SPAN class="keyword token">print</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="string token">'Step 3'</SPAN><SPAN class="punctuation token">)</SPAN>
layer <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>mapping<SPAN class="punctuation token">.</SPAN>Layer<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"Primary"</SPAN><SPAN class="punctuation token">)</SPAN>
layer<SPAN class="punctuation token">.</SPAN>minScale <SPAN class="operator token">=</SPAN> <SPAN class="number token">10000</SPAN>
layer<SPAN class="punctuation token">.</SPAN>showLabels <SPAN class="operator token">=</SPAN> <SPAN class="token boolean">True</SPAN>
arcpy<SPAN class="punctuation token">.</SPAN>mapping<SPAN class="punctuation token">.</SPAN>AddLayer<SPAN class="punctuation token">(</SPAN>df<SPAN class="punctuation token">,</SPAN> layer<SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"AUTO_ARRANGE"</SPAN><SPAN class="punctuation token">)</SPAN>
<SPAN class="line-numbers-rows"><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN></SPAN>