text: from collections import OrderedDict
  
  
  __all__ = ["Pins", "PinsN", "DiffPairs", "DiffPairsN",
             "Attrs", "Clock", "Subsignal", "Resource", "Connector"]
  
  
  class Pins:
      def __init__(self, names, *, dir="io", invert=False, conn=None, assert_width=None):
          if not isinstance(names, str):
              raise TypeError("Names must be a whitespace-separated string, not {!r}"
                              .format(names))
          names = names.split()
  
          if conn is not None:
              conn_name, conn_number = conn
              if not (isinstance(conn_name, str) and isinstance(conn_number, (int, str))):
                  raise TypeError("Connector must be None or a pair of string (connector name) and "
                                  "integer/string (connector number), not {!r}"
                                  .format(conn))
              names = ["{}_{}:{}".format(conn_name, conn_number, name) for name in names]
  
          if dir not in ("i", "o", "io", "oe"):
              raise TypeError("Direction must be one of \"i\", \"o\", \"oe\", or \"io\", not {!r}"
                              .format(dir))
  
          if assert_width is not None and len(names) != assert_width:
              raise AssertionError("{} names are specified ({}), but {} names are expected"
                                   .format(len(names), " ".join(names), assert_width))
  
          self.names  = names
          self.dir    = dir
          self.invert = bool(invert)
  
      def __len__(self):
          return len(self.names)
  
      def __iter__(self):
          return iter(self.names)
  
      def map_names(self, mapping, resource):
          mapped_names = []
          for name in self.names:
              while ":" in name:
                  if name not in mapping:
                      raise NameError("Resource {!r} refers to nonexistent connector pin {}"
                                      .format(resource, name))
                  name = mapping[name]
              mapped_names.append(name)
          return mapped_names
  
      def __repr__(self):
          return "(pins{} {} {})".format("-n" if self.invert else "",
              self.dir, " ".join(self.names))
  
  
  def PinsN(*args, **kwargs):
      pins = Pins(*args, **kwargs)
      pins.invert = True
      return pins
  
  
  class DiffPairs:
      def __init__(self, p, n, *, dir="io", conn=None, assert_width=None):
          self.p = Pins(p, dir=dir, conn=conn, assert_width=assert_width)
          self.n = Pins(n, dir=dir, conn=conn, assert_width=assert_width)
  
          if len(self.p.names) != len(self.n.names):
              raise TypeError("Positive and negative pins must have the same width, but {!r} "
                              "and {!r} do not"
                              .format(self.p, self.n))
  
          self.dir    = dir
          self.invert = False
  
      def __len__(self):
          return len(self.p.names)
  
      def __iter__(self):
          return zip(self.p.names, self.n.names)
  
      def __repr__(self):
          return "(diffpairs{} {} (p {}) (n {}))".format("-n" if self.invert else "",
              self.dir, " ".join(self.p.names), " ".join(self.n.names))
  
  
  def DiffPairsN(*args, **kwargs):
      diff_pairs = DiffPairs(*args, **kwargs)
      diff_pairs.invert = True
      return diff_pairs
  
  
  class Attrs(OrderedDict):
      def __init__(self, **attrs):
          for key, value in attrs.items():
              if not (value is None or isinstance(value, (str, int)) or hasattr(value, "__call__")):
                  raise TypeError("Value of attribute {} must be None, int, str, or callable, "
                                  "not {!r}"
                                  .format(key, value))
  
          super().__init__(**attrs)
  
      def __repr__(self):
          items = []
          for key, value in self.items():
              if value is None:
                  items.append("!" + key)
              else:
                  items.append(key + "=" + repr(value))
          return "(attrs {})".format(" ".join(items))
  
  
  class Clock:
      def __init__(self, frequency):
          if not isinstance(frequency, (float, int)):
              raise TypeError("Clock frequency must be a number")
  
          self.frequency = float(frequency)
  
      @property
      def period(self):
          return 1 / self.frequency
  
      def __repr__(self):
          return "(clock {})".format(self.frequency)
  
  
  class Subsignal:
      def __init__(self, name, *args):
          self.name  = name
          self.ios   = []
          self.attrs = Attrs()
          self.clock = None
  
          if not args:
              raise ValueError("Missing I/O constraints")
          for arg in args:
              if isinstance(arg, (Pins, DiffPairs)):
                  if not self.ios:
                      self.ios.append(arg)
                  else:
                      raise TypeError("Pins and DiffPairs are incompatible with other location or "
                                      "subsignal constraints, but {!r} appears after {!r}"
                                      .format(arg, self.ios[-1]))
              elif isinstance(arg, Subsignal):
                  if not self.ios or isinstance(self.ios[-1], Subsignal):
                      self.ios.append(arg)
                  else:
                      raise TypeError("Subsignal is incompatible with location constraints, but "
                                      "{!r} appears after {!r}"
                                      .format(arg, self.ios[-1]))
              elif isinstance(arg, Attrs):
                  self.attrs.update(arg)
              elif isinstance(arg, Clock):
                  if self.ios and isinstance(self.ios[-1], (Pins, DiffPairs)):
                      if self.clock is None:
                          self.clock = arg
                      else:
                          raise ValueError("Clock constraint can be applied only once")
                  else:
                      raise TypeError("Clock constraint can only be applied to Pins or DiffPairs, "
                                      "not {!r}"
                                      .format(self.ios[-1]))
              else:
                  raise TypeError("Constraint must be one of Pins, DiffPairs, Subsignal, Attrs, "
                                  "or Clock, not {!r}"
                                  .format(arg))
  
      def _content_repr(self):
          parts = []
          for io in self.ios:
              parts.append(repr(io))
          if self.clock is not None:
              parts.append(repr(self.clock))
          if self.attrs:
              parts.append(repr(self.attrs))
          return " ".join(parts)
  
      def __repr__(self):
          return "(subsignal {} {})".format(self.name, self._content_repr())
  
  
  class Resource(Subsignal):
      @classmethod
      def family(cls, name_or_number, number=None, *, ios, default_name, name_suffix=""):
          # This constructor accepts two different forms:
          #  1. Number-only form:
          #       Resource.family(0, default_name="name", ios=[Pins("A0 A1")])
          #  2. Name-and-number (name override) form:
          #       Resource.family("override", 0, default_name="name", ios=...)
          # This makes it easier to build abstractions for resources, e.g. an SPIResource abstraction
          # could simply delegate to `Resource.family(*args, default_name="spi", ios=ios)`.
          # The name_suffix argument is meant to support creating resources with
          # similar names, such as spi_flash, spi_flash_2x, etc.
          if name_suffix:  # Only add "_" if we actually have a suffix.
              name_suffix = "_" + name_suffix
  
          if number is None: # name_or_number is number
              return cls(default_name + name_suffix, name_or_number, *ios)
          else: # name_or_number is name
              return cls(name_or_number + name_suffix, number, *ios)
  
      def __init__(self, name, number, *args):
          super().__init__(name, *args)
  
          self.number = number
  
      def __repr__(self):
          return "(resource {} {} {})".format(self.name, self.number, self._content_repr())
  
  
  class Connector:
      def __init__(self, name, number, io, *, conn=None):
          self.name    = name
          self.number  = number
          mapping = OrderedDict()
  
          if isinstance(io, dict):
              for conn_pin, plat_pin in io.items():
                  if not isinstance(conn_pin, str):
                      raise TypeError("Connector pin name must be a string, not {!r}"
                                      .format(conn_pin))
                  if not isinstance(plat_pin, str):
                      raise TypeError("Platform pin name must be a string, not {!r}"
                                      .format(plat_pin))
                  mapping[conn_pin] = plat_pin
  
          elif isinstance(io, str):
              for conn_pin, plat_pin in enumerate(io.split(), start=1):
                  if plat_pin == "-":
                      continue
  
                  mapping[str(conn_pin)] = plat_pin
          else:
              raise TypeError("Connector I/Os must be a dictionary or a string, not {!r}"
                              .format(io))
  
          if conn is not None:
              conn_name, conn_number = conn
              if not (isinstance(conn_name, str) and isinstance(conn_number, (int, str))):
                  raise TypeError("Connector must be None or a pair of string (connector name) and "
                                  "integer/string (connector number), not {!r}"
                                  .format(conn))
  
              for conn_pin, plat_pin in mapping.items():
                  mapping[conn_pin] = "{}_{}:{}".format(conn_name, conn_number, plat_pin)
  
          self.mapping = mapping
  
      def __repr__(self):
          return "(connector {} {} {})".format(self.name, self.number,
                                               " ".join("{}=>{}".format(conn, plat)
                                                        for conn, plat in self.mapping.items()))
  
      def __len__(self):
          return len(self.mapping)
  
      def __iter__(self):
          for conn_pin, plat_pin in self.mapping.items():
              yield "{}_{}:{}".format(self.name, self.number, conn_pin), plat_pin
  