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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 validate(self, instance, value):
 """Check if value is a valid datetime object or JSON datetime string"""

        if isinstance(value, datetime.datetime):
            return value
        if not isinstance(value, string_types):
            self.error(
                instance=instance,
                value=value,
                extra='Cannot convert non-strings to datetime.',
            )
        try:
            return self.from_json(value)
        except ValueError:
            self.error(
                instance=instance,
                value=value,
                extra='Invalid format for converting to datetime.',
            )