Enclosed {} in Python format strings

[netch80]

Seems apparent, but only after occasionally found this.

>>> "{}".format(math.pi)
'3.141592653589793'
>>> "{:{}}".format(math.pi, 'f')
'3.141593'
>>> "{:{}}".format(math.pi, '.14f')
'3.14159265358979'

>>> f"{math.pi}"
'3.141592653589793'
>>> pr=10
>>> f"{math.pi:.{pr}e}"
'3.1415926536e+00'

And even:

>>> "{:{}}".format(math.pi, '.16e')
'3.1415926535897931e+00'
>>> f"{math.pi:{'.12e'}}"
'3.141592653590e+00'

But this way isnʼt allowed:

>>> f"{math.pi:{\".12e\"}}"
  File "", line 1
    f"{math.pi:{\".12e\"}}"
                           ^
SyntaxError: f-string expression part cannot include a backslash

but we can override it with a trick:

>>> f"{math.pi:{'.12e'}}"
'3.141592653590e+00'
>>> f"""{math.pi:{".12e"}}"""
'3.141592653590e+00'

Not an often case but still useful.