How to make string f-string after variable initiazation?

Question

Let's suppose I get some string and set it to variable - it can't be created as f-string:

str1 = 'date time for {val1} and {val2}'

Then variables inside the string initialized:

val1 = 1
val2 = 77

Calling print(str1) will return 'date time for {val1} and {val2}'. But I would like to get 'date time for 1 and 77'

Is there any function to make a string as a F string? So I want to call something make_F(str1) and get f-string

PS I cant use dict {'val1':1, 'val2':77} with .format because don't know which variables will be needed in the string. I just want magic happen with F-string.

OP made a mistake and didn't assign `val2` in the sample code — Nicolas Gervais, Nov 19 '19 at 15:39
[How do I convert a string into an f-string?](//stackoverflow.com/q/47339121) — 001, Nov 19 '19 at 15:44

score 4 · Accepted Answer · answered Nov 19 '19 at 15:46

4

You need:

str1 = 'date time for {val1} and {val2}'

val1 = 1
val2 = 77

print(eval(f"f'{str1}'"))

answered Nov 19 '19 at 15:46

Mario Camilleri

1,457
11
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Two warnings if you're using this. Firstly, make sure str1 comes from a trusted source, since eval will execute any Python commands contained in it. Secondly, str1 should not be a multi-line string - if it is, then use eval(f'f"""{str1}"""') otherwise eval will throw an EOL error. – Mario Camilleri Nov 19 '19 at 16:25

score 1 · Answer 2 · answered Nov 19 '19 at 15:42

1

You first need to describe variables as e.g

var1 = None
var2 = None

Then you can use it with f-string like this:

x = f'print {var1} and {var2}'

print(x)

And thats it, you will get the result.

answered Nov 19 '19 at 15:42

simkusr

770
2
11
20

How to make string f-string after variable initiazation?

2 Answers2