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

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

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!

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.