I keep getting "invalid \x escape" error in my python code. What am I doing wrong?

Question

I have been trying to get this piece of python code to open a directory on my computer and read its contents, so I can then generate an output for an assignment but I keep getting "invalid \x escape".Is there something wrong with my syntax or are my forward slashes and backslashes all mixed up.

import sys,os,re
import time

define global variables used as counters

tokens = 0
documents = 0
terms = 0
termindex = 0
docindex = 0 

initialize list variable

#

alltokens = []
alldocs = []

#

Capture the start time of the routine so that we can determine the total running

time required to process the corpus

#

t2 = time.localtime() 

set the name of the directory for the corpus

#

dirname = "C:\Users\xhenr\Documents\cs3308\cacm"

For each document in the directory read the document into a string

#

all = [f for f in os.listdir(dirname)]
for f in all:
    documents+=1
    with open('C:\Users\xhenr\Documents\cs3308\cacm/f', 'r') as myfile:
        alldocs.append(f)
        data=myfile.read().replace('\n', '')  
        for token in data.split():
            alltokens.append(token)
        tokens+=1

Open for write a file for the document dictionary

#

documentfile = open('C:/Users/xhenr/Documents/cs3308/cacm/documents.dat', 'w')
alldocs.sort()
for f in alldocs:
  docindex += 1
  documentfile.write(f+','+str(docindex)+os.linesep)
documentfile.close()

#

Sort the tokens in the list

alltokens.sort()

#

Define a list for the unique terms

g=[]

#

Identify unique terms in the corpus

for i in alltokens:    
    if i not in g:
       g.append(i)
       terms+=1

terms = len(g

)

Output Index to disk file. As part of this process we assign an 'index' number to each unique term.

indexfile = open('C:/Users/xhenr/Documents/cs3308/cacm/index.dat', 'w')
for i in g:
  termindex += 1
  indexfile.write(i+','+str(termindex)+os.linesep)
indexfile.close()

Print metrics on corpus

#

print 'Processing Start Time: %.2d:%.2d' % (t2.tm_hour, t2.tm_min)
print "Documents %i" % documents
print "Tokens %i" % tokens
print "Terms %i" % terms

t2 = time.localtime()   
print 'Processing End Time: %.2d:%.2d' % (t2.tm_hour, t2.tm_min)

Answer 1

Here:

dirname = "C:\Users\xhenr\Documents\cs3308\cacm"

Python is interpreting the backslashes as attempts to escape the following character, when actually it's a system path. You can fix this by escaping the backslashes, but there is a much easier method:

dirname = r"C:\Users\xhenr\Documents\cs3308\cacm"

By putting an r in front, you tell Python to treat the string as-is, without any escape characters. (The r stands for raw.) This also means you must change this line, too:

with open('C:\Users\xhenr\Documents\cs3308\cacm/f', 'r') as myfile:

Changed to:

with open(r'C:\Users\xhenr\Documents\cs3308\cacm\f', 'r') as myfile:

(also changed inconsistent use of forward and back slashes.