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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def field2default(self, field):
 """Return the dictionary containing the field's default value Will first look for a `doc_default` key in the field's metadata and then fall back on the field's `missing` parameter. A callable passed to the field's missing parameter will be ignored. :param Field field: A marshmallow field. :rtype: dict """

        ret = {}
        if "doc_default" in field.metadata:
            ret["default"] = field.metadata["doc_default"]
        else:
            default = field.missing
            if default is not marshmallow.missing and not callable(default):
                ret["default"] = default

        return ret