title: Strange dimension change of a nested array after readline and sympify operation?
body: <p>If I understand correctly, in Julia m = [[1,2],[3,4]] is a two-dimensional vector with each vector of two elements. And this fact won't change after the operation of sympify</p>
  <pre><code>ms = sympy.sympify(m)
  size(ms)
  </code></pre>
  <p>The output will still be (2,), as expected.</p>
  <p>However, if I create a file test.txt with just one line [[1,2],[3,4]] and run</p>
  <pre><code>using SymPy
  open(&quot;test.txt&quot;) do io
      while ! eof(io)
          m = readline(io)
          println(m)
          ms = sympy.sympify(m)
          println(ms)
      end
  end
  </code></pre>
  <p>The output will be</p>
  <pre><code>[[1,2],[3,4]]
  Sym[1 2; 3 4]
  </code></pre>
  <p>Namely, now <strong>ms suddenly changes to a two-by-two matrix</strong>! I really cannot understand this (since the dimension of m after readline stays to be (2,) as before). Could someone explain this for me?</p>