Two different week numbers evaluated to same date
<p>I'm parsing weekly time series data from a source that shows dates using a year and week number. However, when trying to use Python's <code>datetime.strptime</code> function to turn these into YYYY-MM-DD dates, two different week numbers sometimes evaluate to the same date, when I know that they should not. The weekly data is for the week ending on a Friday. For example:</p>

<pre><code>datetime.strptime("1998-5-53", "%Y-%w-%U")
Out[43]: datetime.datetime(1999, 1, 8, 0, 0)

datetime.strptime("1999-5-01", "%Y-%w-%U")
Out[44]: datetime.datetime(1999, 1, 8, 0, 0)
</code></pre>

<p>The underlying data from the European Central Bank; an example series is <a href="http://sdw.ecb.europa.eu/quickview.do?SERIES_KEY=123.ILM.W.U2.C.A010.Z5.Z0Z" rel="nofollow">here</a>.</p>
