title: good style to introduce python variables within a loop
body: <p>I have a C++ background and I'm learning Python. I am writing code which needs to extract a particular value from a <code>for</code> loop:</p>
  
  <pre><code>seventh_value = None   # ** my question is about this line
  for index in range(1, 10):
      value = f(index)
      # we have a special interest in the seventh value
      if index == 7:
          seventh_value = value
      # (do other things with value here)
  
  # make use of seventh_value here
  </code></pre>
  
  <p>In C++ I'd need to declare seventh_value before the for loop to ensure its scope is not limited to the for loop. In Python I do not need to do this. My question is whether it's good style to omit the initial assignment to seventh_value.</p>
  
  <p>I understand that if the loop doesn't iterate at least 7 times then I can avoid a NameError by assigning to seventh_value prior to the loop. Let's assume that it is clear it will iterate at least 7 times (as in the above example where I've hard-coded 10 iterations).</p>
  
  <p>I also understand that there may be other ways to extract a particular value from an iteration. I'm really just wondering about whether it's good style to introduce variables before a loop if they will be used after the loop.</p>
  
  <p>The code I wrote above looks clear to me, but I think I'm just seeing it with C++ eyes.</p>