third_party/stdlib/warnings.py
def warn(message, category=None, stacklevel=1):
    """Issue a warning, or maybe ignore it or raise an exception."""
    # Check if message is already a Warning object
    if isinstance(message, Warning):
        category = message.__class__
    # Check category argument
    if category is None:
        category = UserWarning
    assert issubclass(category, Warning)
    # Get context information
    try:
        caller = sys._getframe(stacklevel)
    except ValueError:
        globals = sys.__dict__
        lineno = 1
    else:
        globals = caller.f_globals
        lineno = caller.f_lineno
    if '__name__' in globals:
        module = globals['__name__']
    else:
        module = "<string>"
    filename = globals.get('__file__')
    if filename:
        fnl = filename.lower()
        if fnl.endswith((".pyc", ".pyo")):
            filename = filename[:-1]
    else:
        if module == "__main__":
            try:
                filename = sys.argv[0]
            except AttributeError:
                # embedded interpreters don't have sys.argv, see bug #839151
                filename = '__main__'
        if not filename:
            filename = module
    registry = globals.setdefault("__warningregistry__", {})
    warn_explicit(message, category, filename, lineno, module, registry,
                  globals)
def warn(message, category=None, stacklevel=1):
    """Issue a warning, or maybe ignore it or raise an exception."""
    # Check if message is already a Warning object
    if isinstance(message, Warning):
        category = message.__class__
    # Check category argument
    if category is None:
        category = UserWarning
    assert issubclass(category, Warning)
    # Get context information
    try:
        caller = sys._getframe(stacklevel)
    except ValueError:
        globals = sys.__dict__
        lineno = 1
    else:
        globals = caller.f_globals
        lineno = caller.f_lineno
    if '__name__' in globals:
        module = globals['__name__']
    else:
        module = "<string>"
    filename = globals.get('__file__')
    if filename:
        fnl = filename.lower()
        if fnl.endswith((".pyc", ".pyo")):
            filename = filename[:-1]
    else:
        if module == "__main__":
            try:
                filename = sys.argv[0]
            except AttributeError:
                # embedded interpreters don't have sys.argv, see bug #839151
                filename = '__main__'
        if not filename:
            filename = module
    registry = globals.setdefault("__warningregistry__", {})
    warn_explicit(message, category, filename, lineno, module, registry,
                  globals)
Issue a warning, or maybe ignore it or raise an exception.