擅长:python、mysql、java
<p>阅读<a href="https://docs.python.org/2/library/stdtypes.html#str.count">docs</a>:</p>
<blockquote>
<p>Return the number of (<strong>non-overlapping</strong>) occurrences of substring sub in string <code>s[start:end]</code>. Defaults for start and end and interpretation of negative values are the same as for slices.</p>
</blockquote>
<p>因为“w w”是第一个匹配的,所以它从第三个“w”开始,但无法匹配“ww”。</p>