import math

def archimedes (sides):

      innerangleB = 360.0 / sides
      halfangleA = innerangleB / 2

      onehalfsideS = math.sin(math.radians(halfangleA))

      sideS  =  onehalfsideS * 2

      polygonCircumference = sides * sideS

      polygonCircumference = sides * sideS
      pi = polygonCircumference/2

      return pi

...and here are the errors:

>>> import math
>>>
>>> def archimedes (sides):
...
  File "<stdin>", line 2

    ^
IndentationError: expected an indented block
>>>       innerangleB = 360.0 / sides
  File "<stdin>", line 1
    innerangleB = 360.0 / sides
    ^
IndentationError: unexpected indent
>>>       halfangleA = innerangleB / 2
  File "<stdin>", line 1
    halfangleA = innerangleB / 2
    ^
IndentationError: unexpected indent
>>>
>>>       onehalfsideS = math.sin(math.radians(halfangleA))
  File "<stdin>", line 1
    onehalfsideS = math.sin(math.radians(halfangleA))
    ^
IndentationError: unexpected indent
>>>
>>>       sideS  =  onehalfsideS * 2
  File "<stdin>", line 1
    sideS  =  onehalfsideS * 2
    ^
IndentationError: unexpected indent
>>>
>>>       polygonCircumference = sides * sideS
  File "<stdin>", line 1
    polygonCircumference = sides * sideS
    ^
IndentationError: unexpected indent
>>>
>>>       polygonCircumference = sides * sideS
  File "<stdin>", line 1
    polygonCircumference = sides * sideS
    ^
IndentationError: unexpected indent
>>>       pi = polygonCircumference/2
  File "<stdin>", line 1
    pi = polygonCircumference/2
    ^
IndentationError: unexpected indent
>>>
...       return pi