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 Python Gotchas
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What is the output of the following function?  Why?

::
   >>> def f(x):
   ...     print("3*x = %s" % 3*x)
   >>> f(5)
   3*x = 33*x = 33*x = 33*x = 33*x = 3

Answer: 
   Look at the operator precedence: `%` has higher precedence that `*`, so
   the print statement is parsed as ``print(("3*x = %s" % 3)*x)`` which means,
   print `x` copies of the string.  The fix is recommended in the manual: always
   use a tuple after `%`: ``print("3*x = %s" % (3*x,))``