title: Python 2.7 try and except ValueError
body: <p>I query user input which is expected to be an int by using int(raw_input(...))</p>
  
  <p>However when the user doesn't enter an integer, i.e. just hits return, I get a ValueError.</p>
  
  <pre><code>def inputValue(inputMatrix, rangeRows, rangeCols, defaultValue, playerValue):
      rowPos = int(raw_input("Please enter the row, 0 indexed."))
      colPos = int(raw_input("Please enter the column, 0 indexed."))
      while True:
          #Test if valid row col position and position does not have default value
          if rangeRows.count(rowPos) == 1 and rangeCols.count(colPos) == 1 and inputMatrix[rowPos][colPos] == defaultValue:
              inputMatrix[rowPos][colPos] = playerValue
              break
          else:
              print "Either the RowCol Position doesn't exist or it is already filled in."
              rowPos = int(raw_input("Please enter the row, 0 indexed."))
              colPos = int(raw_input("Please enter the column, 0 indexed."))
      return inputMatrix
  </code></pre>
  
  <p>I tried to be smart and use try and except to catch the ValueError, print a warning to the user and then call the inputValue() again.  Then it works when the user enters return to the query but falls over when the user correctly then enters an integer</p>
  
  <p>Below is the part of the amended code with the try and except:</p>
  
  <pre><code>def inputValue(inputMatrix, rangeRows, rangeCols, defaultValue, playerValue):
      try:
          rowPos = int(raw_input("Please enter the row, 0 indexed."))
      except ValueError:
          print "Please enter a valid input."
          inputValue(inputMatrix, rangeRows, rangeCols, defaultValue, playerValue)   
      try:
          colPos = int(raw_input("Please enter the column, 0 indexed."))
      except ValueError:
          print "Please enter a valid input."
          inputValue(inputMatrix, rangeRows, rangeCols, defaultValue, playerValue)   
  </code></pre>