Now OSError constructor does not support keyword arguments. It will be good add support for followed keyword arguments: "errno", "strerror", "filename". If "strerror" is not specified, a standard error message corresponding to errno is used. If "errno" is not specified for an OSError subclass, an errno associated with this subclass is used (if only one errno associated). For backward compatibility perhaps keyword arguments should be incompatible with any positional arguments (or at least suitable defaults should used only if any keyword argument specified). Examples:

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OSError(errno=errno.ENOENT) FileNotFoundError(2, 'No such file or directory') FileNotFoundError(filename='qwerty') FileNotFoundError(2, 'No such file or directory') FileNotFoundError(strerr='Bad file') FileNotFoundError(2, 'Bad file')