Creating New Type Annotations

Книга: Practical Programming, Fourth Edition

For each built-in type annotation such as int str, list, set, tuple, and dict you can specify the kind of thing it contains. To explore this, let’s revisit atoms and molecules from , using dictionaries and tuples in addition to lists.

Recall functions read_molecule and read_all_molecules; here are the headers and docstrings:

	def read_molecule(reader: TextIO) -> list:
	"""Read a single molecule from reader and return it, or return None to
	signal end of file. The first item in the result is the name of the
	compound; each list contains an atom type and the X, Y, and Z coordinates
	of that atom.

	>>> instring = ('COMPND TEST\\nATOM 1 N 0.1 0.2 0.3\\n' +
	'ATOM 2 N 0.2 0.1 0.0\\nEND\\n')
	>>> infile = StringIO(instring)
	>>> read_molecule(infile)
	['TEST', ['N', '0.1', '0.2', '0.3'], ['N', '0.2', '0.1', '0.0']]
	"""

	def read_all_molecules(reader: TextIO) -> list:
	"""Read zero or more molecules from reader, returning a list of the
	molecule information.

	>>> cmpnd1 = ('COMPND T1\\nATOM 1 N 0.1 0.2 0.3\\n' +
	'ATOM 2 N 0.2 0.1 0.0\\nEND\\n')
	>>> cmpnd2 = ('COMPND T2\\nATOM 1 A 0.1 0.2 0.3\\n' +
	'ATOM 2 A 0.2 0.1 0.0\\nEND\\n')
	>>> infile = StringIO(cmpnd1 + cmpnd2)
	>>> result = read_all_molecules(infile)
	>>> result[0]
	['T1', ['N', '0.1', '0.2', '0.3'], ['N', '0.2', '0.1', '0.0']]
	>>> result[1]
	['T2', ['A', '0.1', '0.2', '0.3'], ['A', '0.2', '0.1', '0.0']]
	"""

Assuming that molecules have unique names, it would make sense for read_all_molecules to return a dictionary where the keys are the names of compounds and the values are the atoms.

Additionally, instead of using a four-item list for atoms, each atom will be represented as a tuple where the first item is the type of the atom and the second item is a tuple of three coordinates.

You can introduce new names for these compound types (pun unintended). Here, let’s define two new types: Atom and CompoundDict:

	Atom = tuple[str, tuple[str, str, str]]
	CompoundDict = dict[str, Atom]

They lead to the new function specifications:

	def read_molecule(reader: TextIO) -> CompoundDict:
	"""Read a single molecule from reader and return it, or return None to
	signal end of file. The returned dictionary has one key/value pair where
	the key is the name of the compound and the value is a list of Atoms.

	>>> instring = 'COMPND TEST\\nATOM 1 N 0.1 0.2 0.3\\n'+\
	'ATOM 2 N 0.2 0.1 0.0\\nEND\\n'
	>>> infile = StringIO(instring)
	>>> read_molecule(infile)
	{'TEST': [('N', ('0.1', '0.2', '0.3')), ('N', ('0.2', '0.1', '0.0'))]}
	"""

	def read_all_molecules(reader: TextIO) -> CompoundDict:
	"""Read zero or more molecules from reader, returning a list of the
	molecule information.

	>>> cmpnd1 = 'COMPND T1\\nATOM 1 N 0.1 0.2 0.3\\n'+\
	'ATOM 2 N 0.2 0.1 0.0\\nEND\\n'
	>>> cmpnd2 = 'COMPND T2\\nATOM 1 A 0.1 0.2 0.3\\n'+\
	'ATOM 2 A 0.2 0.1 0.0\\nEND\\n'
	>>> infile = StringIO(cmpnd1 + cmpnd2)
	>>> result = read_all_molecules(infile)
	>>> result['T1']
	[('N', ('0.1', '0.2', '0.3')), ('N', ('0.2', '0.1', '0.0'))]
	>>> result['T2']
	[('A', ('0.1', '0.2', '0.3')), ('A', ('0.2', '0.1', '0.0'))]
	"""

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