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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 dict_to_schema(schema_dict, required, allow_custom_keys=True, modifier=None):
 """Convert a dict of Schemas into a Schema. Args: required (bool):
 Whether to make schema keys optional or required. allow_custom_keys (bool, optional):
 If True, creates a schema that allows custom items in dicts. modifier (callable):
 Functor to apply to dict values - it is applied via `Schema.Use`. Returns: A `Schema` object. """

    if modifier:
        modifier = Use(modifier)

    def _to(value):
        if isinstance(value, dict):
            d = {}
            for k, v in value.iteritems():
                if isinstance(k, basestring):
                    k = Required(k) if required else Optional(k)
                d[k] = _to(v)
            if allow_custom_keys:
                d[Optional(basestring)] = modifier or object
            schema = Schema(d)
        elif modifier:
            schema = And(value, modifier)
        else:
            schema = value
        return schema

    return _to(schema_dict)