On 13 Sep 2018, at 2:33, Victor Stinner wrote:
Hi,
For the type name, sometimes, we only get a type (not an instance), and we want to format its FQN. IMHO we need to provide ways to format the FQN of a type for *types* and for *instances*. Here is my proposal:
* Add !t conversion to format string * Add ":T" format to type.__format__() * Add "%t" and "%T" formatters to PyUnicode_FromUnicodeV()
As far as I can remember, the distinction between lowercase and uppercase format letter for PyUnicode_FromUnicodeV() and friends was: lowercase letters are for formatting C types (like `char *` etc.) and uppercase formatting letters are for Python types (i.e. the C type is `PyObject *`). IMHO we should keep that distinction.
* Add a read-only type.__fqn__ property
I like that.
# Python: "!t" for instance raise TypeError(f"must be str, not {obj!t}")
/* C: "%t" for instance */ PyErr_Format(PyExc_TypeError, "must be str, not %t", obj);
/* C: "%T" for type */ PyErr_Format(PyExc_TypeError, "must be str, not %T", mytype);
# Python: ":T" for type raise TypeError(f"must be str, not {mytype!T}")
We could solve the problem with instances and classes by adding two new ! operators to str.format/f-strings and making them chainable. The !t operator would get the class of the argument and the !c operator would require a class argument and would convert it to its name (which is obj.__module__ + "." + obj.__qualname__ (or only obj.__qualname__ for builtin types)). So: >>> import pathlib >>> p = pathlib.Path("spam.py") >>> print(f"{pathlib.Path}") <class 'pathlib.Path'> >>> print(f"{pathlib.Path!c}") pathlib.Path >>> print(f"{pathlib.Path!c!r}") 'pathlib.Path' >>> print(f"{p!t}") <class 'pathlib.Path'> >>> print(f"{p!t!c}") pathlib.Path >>> print(f"{p!c}") Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: object is not a class This would also give us: >>> print(f"{p!s!r}") 'spam.py' Which is different from: >>> print(f"{p}") spam.py >>> print(f"{p!r}") PosixPath('spam.py')
Open question: Should we also add "%t" and "%T" formatters to the str % args operator at the Python level?
I have a proof-of-concept implementation: https://github.com/python/cpython/pull/9251
Victor
Servus, Walter