Say I have a function
def foo(): return [1, 2, 3]
I want to interpolate the result of the function into a string to get "001 002 003". I've tried this:
f"{*foo():03d 03d 03d}"
But it produced SyntaxError: can't use starred expression here. Can I do this using an f-string?
is this what you are looking for?
str_repr = ' '.join(map('{:03d}'.format, foo()))
print(str_repr) # prints: 001 002 003
maybe the best thing about this solution is that it works with any list length and with minimal tweaking you can change the output format too.
f"{foo():03d}" would thread over the list.Starred expressions are only allowed in few specific contexts, such as function calls, list/tuple/set literals, etc. An f-string placeholder is not one of them, apparently. You could format each element individually and join the strings, e.g.:
lst = foo()
s = ' '.join(f'{x:03d}' for x in lst) # '001 002 003'
Generally, to format multiple values you have to use a separate placeholder for each value.
The * operator (similar rules exist for **) can only be used inside:
foo(*bar)['foo', *bar]foo, *bar = range(10)It is not an expression and can therefore not be used inside the braces of f-strings.
For lists, f-strings do not seem to add much to what was already possible without them. An alternative, slightly simpler, solution without f-strings and without .join, which works for any list length, is the following
a = foo()
str_repr = ("{:03d} "*len(a)).format(*a)
print(str_repr) # prints: 001 002 003
You can also use the zfill method instead:
s_repr=" ".join([str(x).zfill(3) for x in foo()]) #not very PEP8 =S
f"{' '.join(map('{:03d}'.format, foo()))}"?