List and append elements
<p>Something strange - at least to me - is happening in this snippet of code.</p>

<p>I have a function that I recall from a WS method.
My function is something like this:</p>

<pre><code>try:       
    tipo = d['id_tipo_offerta']
    params = OFFERTA_MAP_DICT[tipo]
    params.append('days_constraints')
except Exception, s:
    self.log_int_raise("core.struttura._parseDictOfferta(): 1 Error=%s", RED(s))
</code></pre>

<p>Omitting the content of <code>OFFERTA_MAP_DICT</code> (in this specific case is an empty list) I want to know why, if I call this function the first time, value of <code>params</code> will be <code>['days_constraints']</code> and every other time I recall still this function, value of params will be <code>['days_constraints','days_constraints',....,'days_constraints']</code> with <em>n</em> elements where <em>n</em> is the number of time that I recall this function.</p>

<p>Is my first assignment done by reference?</p>

<p><strong>Edit</strong>:</p>

<p>Those are my maps</p>

<pre><code>OFFERTA_MAP_DICT= {
        ID_OFFERTA_SCONTOCAMERA:    ID_OFFERTA_SCONTOCAMERA_KEYS,
        ID_OFFERTA_BEFOREDATE:      ID_OFFERTA_BEFOREDATE_KEYS,
        ID_OFFERTA_BEFORENDAYS:     ID_OFFERTA_BEFORENDAYS_KEYS,
        ID_OFFERTA_XFORY:           ID_OFFERTA_XFORY_KEYS,
        ID_OFFERTA_SCALARE:         ID_OFFERTA_SCALARE_KEYS,
        ID_OFFERTA_PACCHETTI:       ID_OFFERTA_PACCHETTI_KEYS,
        ID_OFFERTA_LAST_MINUTE:     ID_OFFERTA_LAST_MINUTE_KEYS,
        ID_OFFERTA_ADVANCE:         ID_OFFERTA_ADVANCE_KEYS
        }


OFFERTA_ROOM_MAP_DICT= {
        ID_OFFERTA_SCONTOCAMERA:    ['id_tipo_sconto', 'valore_sconto', 'id_tipo_prezzo'],
        ID_OFFERTA_BEFOREDATE:      ['id_tipo_sconto', 'valore_sconto', 'id_tipo_prezzo'],
        ID_OFFERTA_BEFORENDAYS:     ['id_tipo_sconto', 'valore_sconto', 'id_tipo_prezzo'],
        ID_OFFERTA_XFORY:           [],
        ID_OFFERTA_SCALARE:         [],
        ID_OFFERTA_PACCHETTI:       ['prezzo'],
        ID_OFFERTA_LAST_MINUTE:     ['id_tipo_sconto', 'valore_sconto', 'id_tipo_prezzo']
        }
</code></pre>
