Python List / Index Query

I am asking a user to enter a number, in which I want to print the item held at that index point in the list..

This is the code i currently have:

List = ["a", "b", "c", "d", "e", "f"]

print "The list has the following", len(List), "list:", List

new_item = 开发者_运维技巧raw_input("Which item would you like to add? ")
List.append(new_item)
print "The list has the following", len(List), "items:", List

Number = raw_input ("Please select a number: ")

Try converting Number to an integer first:

i = int(Number)                                                                 
print "You selected:", List[i]

Incidentally, it's good Python style to make variables lower case, and keep identifiers that begin with a capital letter for classes. So, instead of List you could use my_list and instead of Number just use number. (You shouldn't use list as a variable name since that will hide the built-in list type.)

l = ["a", "b", "c"]
ii = raw_input("Please select a number: ")
print l[ii]

What you are attempting to do is called "indexing" a string. It is achieved as follows

letter_at_index = my_list[index]

Note that indices start from 0, that is,

my_list = ['a', 'b', 'c']
a = my_list[0]
b = my_list[1]
c = my_list[2]

Negative indices can be specified as well, for example

c = my_list[-1]

More info under Sequence Types here

List = ["a", "b", "c", "d", "e", "f"]
print "The list has the following", len(List), "list:", List
try:
    Number = raw_input ("Please select a number: ")
    item = List[int(Number)]
    print "The list item at", Number, "is", item
except EOFError:
    print "Error.  Nothing entered"
except ValueError:
    print "Error.  Expecting a number instead of:", Number
except IndexError:
    print "Error.  Number out of range:", Number

List = ["a", "b", "c", "d", "e", "f"]

print "The list has the following length: "+str( len(List))+ "\n list:"+repr( List)

List.append(raw_input("\nWhich item would you like to add? "))

print "\nThe list has the following length: "+str( len(List))+ "\n list:"+repr( List)

print '\nThe item at the position you entered is : '+\
      repr(List[int(raw_input ("\nPlease select a number: "))])[1:-1]

Result

The list has the following length: 6
 list:['a', 'b', 'c', 'd', 'e', 'f']

Which item would you like to add? (12,52,145)

The list has the following length: 7
 list:['a', 'b', 'c', 'd', 'e', 'f', '(12,52,145)']

Please select a number: 6

The item at the position you entered is : (12,52,145)

try the following:

i = None
listend = len(List)-1
while i == None:
    try:
        print ''
        raw = raw_input("Which item would you like to add? ")
        i = int(raw)
        value = List[i]
    except IndexError:
        print i, 'is out of bounds. Expecting an integer from 0 to', listend 
        i = None
    except:
        print 'You entered "%s" however I was expecting an integer from 0 to %s'%(raw, listend)
    else:
        print 'Result:', List[i]

It is often useful to loop while waiting for acceptable input in this way - you will notice that i is only set to something other than None if int(raw) runs successfully, and if it is out of your list's bounds you set it back to None. The else statement is not strictly necessary as its content could go outside of the while loop, however it seem to be the situation it was designed for - running a block of code only if the try block has not thrown an exception, while not handling exceptions itself.