Crawling directory and listing all datasources using ArcPy?

I'm editing a script to try and create a list of all datasources within MXD's. I've got the script to crawl the file tree and find all the info, but I would like it to output the data for each layer/datasource on a single line, so it is easy to sort in excel.

Can someone take a look at the code I have so far and let me know how to accomplish that?

import arcpy, datetime, os

try:

arcpy.gp.overwriteOutput = True

#Read input parameters from GP dialog

folderPath = arcpy.GetParameterAsText(0)
output = arcpy.GetParameterAsText(1)

#Create an output file
outFile = open(output, "w")

#Loop through each MXD file
count = 0
for root, dirs, files in os.walk(folderPath):
    for filename in os.listdir(folderPath):

      fullpath = os.path.join(folderPath, filename)
      if os.path.isfile(fullpath):
        if filename.lower().endswith(".mxd"):

            #Reference MXD
            mxd = arcpy.mapping.MapDocument(fullpath)
            count = 1

            #Write MXD data to file
            MapDoc = os.path.basename(mxd.filePath)

            MapDocPath = mxd.filePath 

            #Reference each data frame and report data
            DFList = arcpy.mapping.ListDataFrames(mxd)
            for df in DFList:
                #Format output values
                if df.description == "": descValue = "None"
                else: descValue = df.description



                #Reference each layer in a data frame
                lyrList = arcpy.mapping.ListLayers(mxd, "", df)
                for lyr in lyrList:
                    lyrName = lyr.name 
                    if lyr.supports("dataSource"):
                        lyrDatasource = lyr.dataSource                             
                    else: lyrDatasource = "N/A"

            outFile.write("Map Document, MXD Path, DataFrame List, Description, Layer name, Layer Datasource")
            str = ",";

            seq = (MapDoc, MapDocPath, DFList, descValue, lyrName, lyrDatasource);
            outFile.write(str.join(seq))

            del mxd                      

outFile.close()

#Open resulting text file
os.startfile(output)


#Delete variables that reference data on disk
del folderPath, output, outFile, fullpath

except Exception, e:
import traceback
map(arcpy.AddError, traceback.format_exc().split("\n"))
arcpy.AddError(str(e))

The error I recieve when I try to run this is as follows:

\MultiMXDReport_crawl.py", line 60, in 

outFile.write(str.join(seq))
TypeError: sequence item 2: expected string or Unicode, list found
: 'str' object is not callable
Failed to execute (MultiMXDCrawler).