Frozen Record

Some data should never change once it is made: a point on a map, a date, a database row you have already checked. Objects that cannot change are also the only safe dictionary keys and set members. Build a class Record like that.

• Record(**fields) makes a record from keyword arguments, for example Record(name='Ada', year=1815). Fields are read as attributes: r.name. Reading a field that does not exist raises AttributeError.
• Changing a field, adding a new attribute or deleting one (r.year = 1816, r.x = 1, del r.name) raises AttributeError, and the record stays as it was.
• r.replace(**changes) returns a new record with some fields changed, leaving r untouched. A name that is not one of the record's fields raises TypeError.
• r.fields() returns a tuple of the field names in the order they were given.
• Two records are equal (==) when they have the same field names with equal values, in any order. A record is never equal to something that is not a record.
• hash(r): equal records must have equal hashes, and records that differ should almost always have different hashes, so that sets and dicts of records stay fast.
• repr(r) returns the text Record(name='Ada', year=1815): the fields in the order given, each value written with repr.

Examples

r = Record(name='Ada', year=1815)
r.name                                    # returns 'Ada'
r.year = 1816                             # raises AttributeError
r.replace(year=1816)                      # Record(name='Ada', year=1816)
r == Record(year=1815, name='Ada')        # True
len({r, Record(year=1815, name='Ada')})   # 1

Constraints

• Field names are valid Python names and never clash with the method names replace and fields
• All field values in the tests are hashable
• Up to 60,000 records in one test