Setting precision in .format() via use of a variable

Question

If I have the following;

dimensions={
"length" : 1.3576
}

out1 = "l = {length:.3f} mm".format(**dimensions)

However, rather than specifying .3f in the string, I would like to specify it via a variable.
The following does work:

precision=".2f"
out2 = "l = {length:"+str(precision)+"} mm"
print(out2)
out2=out2.format(**dimensions)
print(out2)

gives:

l = {length:.2f} mm
l = 1.36 mm

But this feels like a hacky job of it. Is there a better way?

Answer 1

You can nest substitutions for formatting:

>>> precision = '.3f'
>>> out1 = "l = {length:{precision}} mm".format(precision=precision, **dimensions)
>>> out1
'l = 1.358 mm'

the syntax looks a little strange but totally works!