ArcGIS desktop won't import arcpy

Question

I have arcgis 10.3 and I am trying to run a task using python but the python window within arcmap won't import arcpy. This never happened to me with 10.2.2. The error returned is:

Runtime error 
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\__init__.py", line 24, in <module>
    from arcpy.toolbox import *
  File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\toolbox.py", line 15, in <module>
    from .ddd import ASCII3DToFeatureClass as ASCII3DToFeatureClass_3d
  File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\ddd.py", line 23, in <module>
    from arcpy.arcobjects.arcobjectconversion import convertArcObjectToPythonObject
  File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\arcobjects\__init__.py", line 19, in <module>
    arcobjectconversion.initialize_conversion_mapping()
  File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\arcobjects\arcobjectconversion.py", line 26, in initialize_conversion_mapping
    from .._mapping import MapDocument, PageLayout, DataFrame, DataFrameTime, DataDrivenPages, \
  File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\_mapping.py", line 19, in <module>
    from arcpy.utils import logcall, ArgAdaptor
  File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\utils.py", line 17, in <module>
    import inspect
ImportError: No module named inspect

Answer 1

If I was receiving this error then I would suspect a corrupt installation.

The expedient to resolving it, especially on a weekend, may be to uninstall ArcGIS for Desktop, remove any traces of Python from your machine, and then reinstall ArcGIS for Desktop which should reinstall Python cleanly.

Answer 2

I had this exact issue - I renamed the folder "C:\Python27" to "C:\Python27_old" and then repaired the ArcGIS Desktop installation from Control Panel, Programs and Features (Win7); highlighting "ArcGIS 10.3.1 for Desktop", and then Clicking "Install/Change" and selecting "Repair". Worked for me, and faster than reinstalling everything.