recwarn.py 文件源码

def __enter__(self):
        if self._entered:
            __tracebackhide__ = True
            raise RuntimeError("Cannot enter %r twice" % self)
        self._entered = True
        self._filters = self._module.filters
        self._module.filters = self._filters[:]
        self._showwarning = self._module.showwarning

        def showwarning(message, category, filename, lineno,
                        file=None, line=None):
            self._list.append(RecordedWarning(
                message, category, filename, lineno, file, line))

            # still perform old showwarning functionality
            self._showwarning(
                message, category, filename, lineno, file=file, line=line)

        self._module.showwarning = showwarning

        # allow the same warning to be raised more than once

        self._module.simplefilter('always')
        return self