format() on a string with a math expression inside brackets in python

Question

Is there a way to get the same result using .format()?

a = 10
print(f'something {a+2}')
something 12

When I try to do it like this I get KeyError:

print('something {a+2}'.format(a=10))
KeyError                                  
Traceback (most recent call last)
<ipython-input-94-69f36f3c6aec> in <module>
----> 1 'something {a+2}'.format(a=10)

KeyError: 'a+2'

`print('something {a}'.format(a=10+2)`, just do the operation outside — Netwave, Nov 14 '19 at 14:48
like this? `print('something {}'.format(a+2))` It seems like you have something specific in mind. — Nicolas Gervais, Nov 14 '19 at 14:48
Netwave, none of your 8 edits (and deleted answers) have worked so far... — Nicolas Gervais, Nov 14 '19 at 14:48
@NicolasGervais, yeah, I did not read the question properly. — Netwave, Nov 14 '19 at 14:49
If you added one more parenthesis, your comment above would work, however. — Nicolas Gervais, Nov 14 '19 at 14:51
f-strings work differently than format. With an f-string you can do it as the first example but with format you need to do something like the examples in the comments above. — Error - Syntactical Remorse, Nov 14 '19 at 14:51
@Netwave Yeah, I know that will work, but I'd need to rewrite a bunch of code to be able to do that. So I hoped there's a way not to do that — Михаил Нефедов, Nov 14 '19 at 14:56
I would also encourage you to use f-strings whenever possible :) — AMC, Nov 14 '19 at 15:22

drt · Answer 1 · 2019-11-14T16:09:45.387

0

Python 3.8 new feature (Walrus)

a = 10
print(f'something {(result:=a+2)}')

Python 3.7

print(f'something {(a+2)}')
print(f'something {a + 2}')
print('something {a}'.format(a=10 + 2))
print('something {}'.format(a+2))

Updated all above options (Just to match OP's expectations)

edited Nov 14 '19 at 16:09

answered Nov 14 '19 at 15:23

drt

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The OP was asking more about `format` and less about f-strings. `f"{a+2}"` works with f-strings. Though using walrus for 3.8 the example is an interesting idea. – Error - Syntactical Remorse Nov 14 '19 at 15:57
Uh! I missed that – drt Nov 14 '19 at 16:06

score 0 · Answer 2 · answered Jul 16 '23 at 04:20

0

You may consider this solution: https://stackoverflow.com/a/53671539/4563935

This works for your example:

def fstr(template):
    return eval(f"f'{template}'")

a = 10
template = "something {a + 2}"
print(fstr(template))
# Output: something 12

answered Jul 16 '23 at 04:20

Ray

170
3
10

format() on a string with a math expression inside brackets in python

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