The simplest way to transform coordinates in Python is pyproj, i.e. the Python interface to PROJ.4 library. In fact:
from pyproj import Proj, transform
inProj = Proj(init='epsg:3857')
outProj = Proj(init='epsg:4326')
x1,y1 = -11705274.6374,4826473.6922
x2,y2 = transform(inProj,outProj,x1,y1)
print x2,y2
returns
-105.150271116 39.7278572773
For instance you can use the GDAL Python bindings to convert this point from the projected coordinate system (EPSG 3857) to a geographic coordinate system (EPSG 4326).
import ogr, osr
pointX = -11705274.6374
pointY = 4826473.6922
# Spatial Reference System
inputEPSG = 3857
outputEPSG = 4326
# create a geometry from coordinates
point = ogr.Geometry(ogr.wkbPoint)
point.AddPoint(pointX, pointY)
# create coordinate transformation
inSpatialRef = osr.SpatialReference()
inSpatialRef.ImportFromEPSG(inputEPSG)
outSpatialRef = osr.SpatialReference()
outSpatialRef.ImportFromEPSG(outputEPSG)
coordTransform = osr.CoordinateTransformation(inSpatialRef, outSpatialRef)
# transform point
point.Transform(coordTransform)
# print point in EPSG 4326
print point.GetX(), point.GetY()
This returns for your point the coordinates of
-105.150271116 39.7278572773