# 
# file: read-from-file-mod4.py
# This program asks the user to type the file name to be opened
# Opens the file, and displays all the data from the file on the screen.
# After that it finds the sum of numbers, and displays it on the screen.
# !!! Please, note the the input file "numbers.dat" should be stored in the
#     same place your program is.
#
# The program uses readlines() function
#

def main():
    print "This program opens a file with numbers, displays all the information on the screen, and "
    print "finds the sum of all the numbers."
    print "Please, note that the file should have one number per line, e.g.:"
    print "5 \n6 \n7 \n12 \n-19 \n6 \n"

    fname=raw_input("Please, input the name of a file you'd like to work with:")

    try: # if the try fails because of IOError,
         #then we will output the warning and stop the program
        in_stream=open(fname,"r")

        strngs=in_stream.readlines() # strngs is a list of strings,
      # each element refers to the corresponding line of charactes in the input file,
      # i.e. the 0th element refers to the first line, the 1st to the second, and so forth

        # let's find out how many lines/strings/numbers are there
        n=len(strngs)

        sum=0 # initially the sum is zero
        for i in range(n):
            try:    # this is the place where we ignore symbols, that are not numbers
                # conversion of a string to an integer value
                next_number=int(strngs[i]) 
                sum=sum+next_number # updating the sum
            except:
                flag=1
            
        print "The contents of the file %s is:" % (fname)
        for i in range(n):
            if i!=n-1:
                print strngs[i][:-1]
            else:
                print strngs[i]
                
        print "The sum of all numbers is %d. Good buy!" % (sum)

    except IOError:
        print "Cannot open the file %s." % (fname)
    
main()