Summary
When used with the Describe function, a file returns a dataType of "File".
Code sample
The following stand-alone script displays some Describe Object Properties for a file.
import arcpy
# Create a Describe object
#
desc = arcpy.Describe("C:/data/Install.log")
# Print some Describe Object properties for the file
#
print "Data Type: " + desc.dataType
print "Path: " + desc.path
print "Base Name: " + desc.baseName
print "Extension: " + desc.extension