Get joined string from list of lists of strings in Python
<p>I have a list of lists and a separator string like this:</p>

<pre><code>lists = [
    ['a', 'b'],
    [1, 2],
    ['i', 'ii'],
]
separator = '-'
</code></pre>

<p>As result I want to have a list of strings combined with separator string from the strings in the sub lists:</p>

<pre><code>result = [
    'a-1-i', 
    'a-1-ii', 
    'a-2-i', 
    'a-2-ii',
    'b-1-i', 
    'b-1-ii', 
    'b-2-i', 
    'b-2-ii',
]
</code></pre>

<p>Order in result is irrelevant.</p>

<p>How can I do this?</p>
