Python List / Index Query

Question

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 = 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: ")

Answer 1

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.)

Answer 2

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

Answer 3

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

Answer 4

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

Answer 5

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)

Answer 6

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.