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Python Python Basics (Retired) Putting the "Fun" Back in "Function" Functions

Timothy Comeau
Timothy Comeau
3,710 Points

Stuck on Challenge of Python functions

Ok, now I'm stuck on question 2.

This code works outside of the Challenge interpreter to deliver the requested result.

Question 1 is: Make a function named add_list that adds all of the items in a passed-in list together and returns the total. Assume the list contains only numbers. You'll probably want to use a for loop.

and it's accepted answer is:

list=[1,2,3]

def add_list(list):
    sum = 0 
    for num in list:
        sum = sum + num
    return sum

b= add_list(list)
print(b)

Question 2 is: Now, make a function named summarize that also takes a list. It should return the string "The sum of X is Y.", replacing "X" with the string version of the list and "Y" with the sum total of the list.

list=[1,2,3]

def add_list(list):
    sum = 0 
    for num in list:
        sum = sum + num
    return sum

b= add_list(list)
print(b)

#Q2 answer

def summarize(list,b):
    a=str(list)
    print("The sum of {} is {}".format(a,b))

c = summarize(list,b)

and this outputs

The sum of [1,2,3] is 6

but the challenge interpreter throws a "summarize() missing 1 required positional argument: 'b'" error and if I modify it I get a "no longer passing error"

6 Answers

Kenneth Love
STAFF
Kenneth Love
Treehouse Guest Teacher

You've said that summarize takes two arguments, list and b. When I call summarize to check your work, I only pass in one argument, the list I want summarized. That's why you're getting that error.

On a side note, you don't want to name a variable list (or str or dict or...you get the idea) as that'll make it hard for you to do list() to turn something, say a string, into a list.

Timothy Comeau
Timothy Comeau
3,710 Points

Ok, noted about the bad name for the list variable.

So I'm trying to call variable b because it contains the function add_list and its output/result. So I'm thinking that to run summarize, I need to pass in list (to turn it to a string) and add_list - but can I pass in a function as an argument to another function? I.E. ...

def summarize (list, add_list()): 

??

Kenneth Love
Kenneth Love
Treehouse Guest Teacher

Don't try to call functions as arguments when creating functions because that won't work.

But you can call functions as arguments to other functions or inside of functions.

add(int('1'), int('2'))

Or

def foo():
    a = int('1')

Are both valid.

Timothy Comeau
Timothy Comeau
3,710 Points

Sorry clicking on "add a comment" turned that into "best answer"

I don't understand what you're saying above, since it seems to be contradictory. You're saying 1) Don't call functions as arguments when creating functions, but 2) call functions as arguments. ???? What is the difference.

I'm running solutions ideas on my own Terminal and default Mac Python and like above, I found this script will also return the expected result. but when I run it in the code interpreter, I once again get a "no longer passing error";

ex_list=[1,2,3]

def add_list(ex_list):
    sum = 0 
    for num in ex_list:
        sum = sum + num
    return sum

print(add_list(ex_list))

def summarize():
    a= add_list(ex_list)
    print("The sum of {} is {}".format(ex_list,a))

print(summarize())

But I'm also getting the None error when I run the script

6
The sum of [1, 2, 3] is 6
None
Kenneth Love
Kenneth Love
Treehouse Guest Teacher

Let's see if this helps explain it a bit better.

Defining a function

def my_function(var1, var2):
    print('you called me with {} and {}'.format(var1, var2))

I've created a function using the def (short for "define") keyword. I've said the function takes two arguments.

Calling a function

my_function(str(100), str(200))

Here I've called the function named my_function and given it the two arguments it expects. Each of my arguments to it, though, are actually calling the str() function, too.


So you can call functions as arguments to another function, but you can't call a function when you're defining a function.


Also, your summarize() function doesn't take any arguments, so it doesn't get a list to summarize, it always works on the ex_list variable that you create at the top. That won't pass the test and wouldn't be a very useful function in the real world.

This worked for me.

def summarize(list):
  return "The sum of {} is {}.".format(str(list), sum(list))

in this challenge, in task 2, I've wrote this code:

list=[1,2,3]

def add_list(list): sum = 0 for num in list: sum = sum + num return sum

def summarize(): return "The sum of {} is {}".format(str(list).strip('[]'), add_list(list))

sum = summarize()

print (sum)

my output is: The sum of 1, 2, 3 is 6

and I get this error message: "Oops! It looks like Task 1 is no longer passing."

Where or which is my error? thanks.

i tried this and tried every thing on google etc. i need help please

Kenneth Love
Kenneth Love
Treehouse Guest Teacher

We can't really help you without seeing your code.

well how do i show it kenneth love

Kenneth Love
Kenneth Love
Treehouse Guest Teacher

Copy it from the code challenge and paste it into a comment/answer box on this thread or start a new thread with it. Put three backticks (```) and the word "python" before the code, and three more backticks at the end of it. It'll be something like:

```python
def hello():
    print("hello")
` ` `

but without the spaces in the last set of backticks.

Shea Taylor
PLUS
Shea Taylor
Courses Plus Student 664 Points

I know this is an old question... but I had some trouble with it myself and thought I'd revive it. Why not solve with the sum function? Like so:

my_list = [1, 2, 3]
total = sum(my_list)

def add_list(my_list):
  return total
print(add_list(my_list))


def summarize(my_list):
  return "The sum of {} is {}.".format(str(my_list), total)
print(summarize(my_list))

This is what ultimately worked for me. Thoughts? What would be the benefit of a for loop in this situation?

Kenneth Love
Kenneth Love
Treehouse Guest Teacher

Your solution assumes that my_list and total would be available. Think about if you were writing this as a standalone function where the function's arguments would be coming from somewhere else, not sitting in the same file.

Also, the point of the exercise is to build your own version of sum, effectively.

Shea Taylor
Shea Taylor
Courses Plus Student 664 Points

Kenneth Love I appreciate the response! I'm pretty new to coding, so forgive my ignorance. I see what you're saying, but how would I code this function without referencing my_list? I know how to build my own version of sum into the function, but I'm not sure how to code it to take an argument outside of the file. What do we put in the parentheses if we wanted to make it standalone?

def add_list(???):
Kenneth Love
Kenneth Love
Treehouse Guest Teacher

Shea Taylor You put what you want the argument to be called inside of the function.

def add_list(list_to_add):
def add_list(bucket_list):
def add_list(stuff):

Whatever you call the argument is what its value will be known as inside of the function.