[Python-Dev] bpo-34595: How to format a type name?

Victor Stinner vstinner at redhat.com
Wed Sep 12 20:33:23 EDT 2018


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

* Add !t conversion to format string
* Add ":T" format to type.__format__()
* Add "%t" and "%T" formatters to PyUnicode_FromUnicodeV()
* Add a read-only type.__fqn__ property

# 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}")

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:



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