from migen import *

class LEDBlinker(Module):
    def __init__(self):
        self.led = Signal()

        ###

        counter = Signal(26)
        self.comb += self.led.eq(counter[25])
        self.sync += counter.eq(counter + 1)

if __name__ == "__main__":
    from migen.fhdl.verilog import convert
    m = LEDBlinker()
    convert(m, ios=set(m.led)).write("ledblinker.v")

#######################################

$ python3 ledblinker.py
Traceback (most recent call last):
  File "ledblinker.py", line 16, in <module>
    convert(m, ios=set(m.led)).write("ledblinker.v")
  File "~/projects/whitequark/mvenv/lib/python3.6/site-packages/migen-0.5.dev0-py3.6.egg/migen/fhdl/structure.py", line 131, in __hash__
    raise TypeError("unhashable type: '{}'".format(type(self).__name__))
TypeError: unhashable type: '_Slice'