[Tutor] Test for type(object) == ???

[eryk sun]

On Sat, Feb 11, 2017 at 3:22 AM, boB Stepp <robertvstepp at gmail.com> wrote:
>
> py3: help(repr)
> Help on built-in function repr in module builtins:
>
> repr(obj, /)
>     Return the canonical string representation of the object.
>
>     For many object types, including most builtins, eval(repr(obj)) == obj.
>
> Question:  What does the forward slash represent in this context?

It's from the function's __text_signature__.

    >>> repr.__text_signature__
    '($module, obj, /)'

It means "obj" is a positional-only argument that cannot be passed as a keyword.

    >>> s = inspect.signature(repr)
    >>> s.parameters['obj'].kind
    <_ParameterKind.POSITIONAL_ONLY: 0>

CPython has a lot of built-in functions that don't allow keyword arguments.

    >>> repr(obj=42)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: repr() takes no keyword arguments

Look at open() for comparison.

    >>> open.__text_signature__
    "($module, /, file, mode='r', buffering=-1, encoding=None,\n
    errors=None, newline=None, closefd=True, opener=None)"

All of its parameters can be passed as keyword arguments.

    >>> s = inspect.signature(open)
    >>> s.parameters['file'].kind
    <_ParameterKind.POSITIONAL_OR_KEYWORD: 1>
    >>> s.parameters['mode'].kind
    <_ParameterKind.POSITIONAL_OR_KEYWORD: 1>

For example:

    >>> open(file='spam', mode='w')
    <_io.TextIOWrapper name='spam' mode='w' encoding='UTF-8'>