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Python Python Collections (Retired) Dictionaries Unpacking Dictionaries

Posted by underfish
underfish
3,226 Points

It doesn't seem like you can use numbers as keys when formatting with kwargs. Am I doing this wrong or is this the case?

I recognize they are "keyword" args, but it still seems strange you can't use numbers (and I'm not sure what else) to format.

Example:

# throws IndexError: tuple index out of range
my_dict = {1: 'a', 2: 'b'}
my_string = "{1} comes before {2}."
my_string.format(**my_dict)

# works
my_dict = {'one': 'a', 'two': 'b'}
my_string = "{one} comes before {two}."
my_string.format(**my_dict)

Is there a way to escape the numbers in my_string?

[MOD: fix formating -cf]

1 Answer

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,457 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,457 Points

In short, you cannot escape numbers to use as named fields.

The issue is using named fields vs positional fields. When format sees a field with a number, such as {1}, it expects positional list of arguments to fill the fields. This is useful if you have a repeated field:

>>> "{0} {1} {0}".format("Department", "Redundancy")
'Department Redundancy Department'

Using a positional unpacking works:

>>> my_string = "{0} comes before {1}."
>>> my_list = ['a', 'b']
>>> my_string.format(*my_list)
'a comes before b.'

EDIT: thought of an additional way to use a dictionary:

>>> my_dict = {0: 'a', 1: 'b'}
# Change field names to expect dictionary
>>> my_string = "{dct[0]} comes before {dct[1]}."
>>> my_string.format(dct=my_dict)
'a comes before b.'

Other usage examples in the docs

underfish
underfish
3,226 Points

Awesome, thanks.