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<p>输入</p>
<pre><code>[['1','2','3'],['a','b','c'],['6','7','8'],['e','f','g']]
</code></pre>
<p>输出应为:</p>
^{pr2}$
<p>代码:</p>
<pre><code>def print_row(los):
print ', '.join(los)
def print_table(los):
lose = []
if los == []:
return
else:
return print_row(los[0]) + print_table(los[1:])
</code></pre>
<p>目前:</p>
<pre><code>print_table([['1','2','3'],['a','b','c'],['6','7','8'],['e','f','g']])
</code></pre>
<p>给出:</p>
<pre>
1, 2, 3
a, b, c
6, 7, 8
e, f, g
TypeError: unsupported operand type(s) for +: 'NoneType' and 'NoneType'
</pre>
<p>我怎么解决这个问题?在</p>