Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

Python Python Collections (2016, retired 2019) Dictionaries String Formatting with Dictionaries

Ronald Tse
Ronald Tse
5,798 Points
Posted by Ronald Tse
Ronald Tse
5,798 Points

Confusing with pack and unpack

it keeps saying "format() argument after ** must be a mapping, not list"

What does it mean?

string_factory.py 
# Example:
values = [{"name": "Michelangelo", "food": "PIZZA"}, {"name": "Garfield", "food": "lasagna"}]
# string_factory(values)
# ["Hi, I'm Michelangelo and I love to eat PIZZA!", "Hi, I'm Garfield and I love to eat lasagna!"]

template = "Hi, I'm {name} and I love to eat {food}!"

def string_factory(values):
    result_list = []
    for value in values:
        result_list.append(template.format(**values))
    return result_list

2 Answers

Torsten Lundahl
Torsten Lundahl
2,570 Points
Torsten Lundahl
Torsten Lundahl
2,570 Points

You are formatting the string using 'values' instead of 'value'. 'values' is refering to the list, and 'value' is refering to the dict inside of that list. In other words your code is trying to unpack a list, when it is expecting to unpack a dictionary. Change 'values' to 'value' inside of format() and your code should work fine!

markmneimneh
markmneimneh
14,132 Points
markmneimneh
markmneimneh
14,132 Points

Hello

Try this and see if it will point you into the right direction

values = [{"name": "Michelangelo", "food": "PIZZA"}, {"name": "Garfield", "food": "lasagna"}]
# string_factory(values)
# ["Hi, I'm Michelangelo and I love to eat PIZZA!", "Hi, I'm Garfield and I love to eat lasagna!"]

template = "Hi, I'm {} and I love to eat {}!"

def string_factory(values):
    result_list = []
    for dict in values:
        result_list.append(template.format(dict['name'], dict['food']))
    return result_list


print(string_factory(values))

if this answers your question, please mark question as answered.