variables in f-string

[Skaperen]

is it OK to set variables in an f-string? i need to call an expensive (e.g. slow) function to get a value that is needed in 3 places in an f-string and again in a 2nd f-string. calling this function 4 times is bad and also can cause other problems. currently i call it once and assign its return value to a short variable and use that in the f-strings. now i'm wanting to squeeze this into one line:
[stupid example code]

print(f'{x=stupid_slow_function()} {x} {x} {x}',some_other_big_string,f'foo{x}bar}')

[/stupid example code]

[mdlatt]

Replace '=' with the walrus operator := and wrap the assignment parentheses. So ...

print(f'{(x:=stupid_slow_function())} {x} {x} {x}',some_other_big_string,f'foo{x}bar}')

[Skaperen]

what is the difference between = and :=?

[Skaperen]

ah, the disadvantage of using 3.7 documentation. gotta fix that.