What is the proper way to take a directory path as user input?

Question

Below is a snippet of code I am trying to use to take a directory path as "raw input" from the user. I receive the following error after the input is taken from the user:

Traceback (most recent call last):
  File "C:\Users\larece.johnson\Desktop\Python Programs\Hello World 2", line 14, in <module>
    f = open(str,"r+")                                     #I open the text file here which the user gave me
IOError: [Errno 2] No such file or directory: 'C:/Users/larece.johnson/Desktop/Python Programs/BostonLog.log.2014-04-01'

Ignoring what I have done below, is there a particular way I am supposed to take the path from user so that Python accepts it?

For example, the directory and file I'm looking for is

C:/Users/larece.johnson/Desktop/Python Programs/BostonLog.log.2014-04-01

import re     #this library is used so that I can use the "search" function
import os     #this is needed for using directory paths and manipulating them 

str =""       #initializing string variable for raw data input

#print os.getcwd()
#f = open("C:/Users/larece.johnson/Desktop/BostonLog.log.2014-04-02.log","r+")

str = raw_input("Enter the name of your text file - please use / backslash when typing in directory path: ");  #User will enter the name of text file for me

f = open(str,"r+")

Answer 1

I think you should try something like:

import sys
import os

user_input = raw_input("Enter the path of your file: ")

assert os.path.exists(user_input), "I did not find the file at, "+str(user_input)
f = open(user_input,'r+')
print("Hooray we found your file!")
#stuff you do with the file goes here
f.close()