User input average

The main functions that are going to be useful to you here are sum() and len()

sum() returns the the sum of items in a iterable

len() returns the length of a python object

Using these functions, your case is easy to apply these too:

my_list = []
plus_one = []

for x in range(5):
    my_list.append(x)
    plus_one.append(x+1) 

print my_list
print plus_one

def average():
    average = sum(my_list) / len(my_list) 
    return average

print average()

As Shashank pointed out, the recommended way is to define a parameter in the function and then pass the argument of your list when calling the function. Wasn't sure if you had learned about parameters yet, so I originally left it out. Here it is anyway:

def average(x):
    # find average of x which is defined when the function is called

print average(my_list) # call function with argument (my_list)

The benefit of this is if you have multiple lists, you don't need a new function, just change the argument in the function call.

You can simply use avg = sum(my_list)/len(my_list) if (len(my_list) != 0) else 0 to get your average if you want to use the library functions.

Otherwise, if you just want to know how to change your code, take a look at the error it generates:

Traceback (most recent call last):
  File "file.py", line 12, in <module>
    average(my_list)
TypeError: average() takes no arguments (1 given)

Obviously, we need to pass in the list to average. Here's a very naive way of computing the average

def average(l):
  s =0
  c = 0
  for val in l:
    s += val
    c +=1
  avg = (s/c if (c != 0)  else 0)
  print("the average of your numbers is: " +str(avg)+ ".")

This could be easily replaced by my earlier code:

def avg(l):
  avg = sum(l)/len(l) if (len(l) != 0) else 0
  print("the average of your numbers is: " +str(avg)+ ".")
  # or
  if (len(l) !=0):
    avg = sum(l)/len(l)
  else:
    avg = 0
  print("the average of your numbers is: " +str(avg)+ ".")

The solution I provided makes use of Python 3, which you appear to be using.

    #!/usr/bin/env python3

    """The segment below takes user input for your list."""

    userInput = input("Enter a comma-delimited list of numbers \n")
        userList = userInput.split(",")
        try:
            data_list = [float(number) for number in userList]
        except ValueError:
            print("Please enter a comma-delimited list of numbers.")


    def list_modifier(list_var):
       """Print the original list, average said list, modify it as needed,
          and then print again."""
       print("Your list is: " + list_var)
       average = sum(list_var) / len(list_var)  # Divide list by sum of elements
       for x in list_var:
            x += 1
       print("Your modified list is: " + list_var)

    list_modifier(data_list)

I used a little bit of fancy stuff to take the user input that handles errors if they arise, but really you should not be worrying about stuff like that.

The split() string method just splits up strings into a list of individual smaller strings using whatever parameter you give it. In this case, I split it up on every comma. I added error handling because if you end a string in a comma, the input function will not work.

I also made use of list comprehension, a type of expression in python that creates lists based on the parameters passed within the brackets. This is seen in the code below:

[float(number) for number in userList]

This takes each string within the list of strings created by split() and makes it into a number. We now have our desired list of numbers.

Beyond that, we have the list_modifier function, which first states the list of numbers with string concatenation. It then uses the sum() function to find the sum of all of the elements of the list and divides that sum by the length of the list.

The for code block takes each element in the list and adds one to it. String concatenation is used once again to finally show our modified list.

I really hoped this solution helped, sorry if it was a bit overly-complex. Try/except blocks can be quite useful for handling errors, I really recommend you look into them later on. See the Python documentation as well if you want to get ahead in class.

Good luck and have fun!