1.  (i), (ii), (iv)

2.  

def checkForFile(userArg,dr,flst):
   if userArg[1]: return
   check = map(lambda x: x == userArg[0],flst)
   if sum(check) > 0: userArg[1] = True
   return 

def findFile(fname):
   userArg = [fname,False]
   os.path.walk('.',checkForFile,userArg)
   return userArg[1]
                   
import os           
print findFile('w')
print findFile('w1')
print findFile('ww')

3.

def makeLineIdx(fname):
   f = open(fname)
   lns = f.readlines()
   lens = map(len,lns)
   idxs = [0]
   tot = 0
   for i in range(len(lns)-1):
     tot += lens[i]
     idxs.append(tot)
   return idxs

def midReadLines(fname,fnameIdx,startLine):
   f = open(fname)
   f.seek(fnameIdx[startLine])
   return f.readlines()

idx = makeLineIdx('x')
print idx
print midReadLines('x',idx,1)