ITEC 109 2014spring ibarland

home—info—labs—exams—hws
—D2L—MediaSamples/—breeze (snow day)—tutor/PIs

lab15-print
print
and, finish lab 14

Last time, we saw how we can turn our code into functions, using “def”. We will spend today finishing your work on that lab.

One new concept: the function print. Just like we saw show, a function which took in a picture object and drew some pixels on the screen (but didn't actually return a result), print is the corresponding function which prints to the “standard output” (which is the lower pane in JES, if you call the function from the lower pane). It does not return a value.

Example:

print( "hello" )
print( "hi t" + "here")

print( ruUserName("James Fallon") )
print( "Jimmy Fallon's name at RU is " + ruUserName("James Fallon") + ".")
    

Note that print wants to be given a string. If you give it a number, it will convert automatically. But if you want to concatenate a string with a number, you must convert the number yourself. The function str : float -> string does this: str(3.7000) = "3.7", and str(0123) = "123".

Example:

print( "The BMI of the penguin is dangerously high: " + str( bmi(220,3,3.2) ) )
    

Be aware:

The print function does not give back an answer; it just changes some pixels on the screen. In particular, the following does not make sense: len( print("hello") ). Moreover, if ruUserName had just printed its result (rather than return it), we couldn't even ever compute len( ruUserName( "Jay Leno" ) ).

In general, printing does not “play well with other functions”. Most functions should return their answer, and not print them; we'll wrap the “real” functions with code that prints out the results, when we want to see a particular result (as opposed to further-processing-the-result).

Printing your results

When you Load a program that is in the editor pane, and 'print' statements are discarded¹. But if you call a function from the interaction pane (bottom), any print statements do get printed down in that interaction pane. SO, Here's the approach we'll take:

• As always, write your functions in the editor pane, and have them return answers — not print.
• We'll make one additional function at the end of the editor pane, we'll always call it “tst”, whose purpose is just to call our other functions and print the results.
• Your function tst should be the only function with a print statement — all other “real” functions should return an answer.
• Down in the interactions pane, to check off, we'll just have you run tst().

# Editor pane:

# ruUserName : string -> string
# Return the RU username, for somebody with the given `fullName`.
#
def ruUserName( fullName ):
  firstInit = substring(fullName,0,1)
  startLast = string.find( fullName, " " ) + 1   # last-name starts 1 char *after* the space.
  lastName = substring(fullName, startLast, len(fullName))
  return string.lower( firstInit + lastName )
  

# triple: float -> float
# Triple a number.
#
def triple( x ):
  return x * 3

# tst : None -> None
# Call/test the above function, printing some results.
#
def tst():
  print( "user name for Walter Mitty: " )
  print( "Expect: " + "wmitty" )
  print( "Actual: " + ruUserName("Walter Mitty") )

  print( "user name for Jay Z: " )
  print( "Expect: " + "jz" )
  print( "Actual: " + ruUserName("Jay Z") )

  print( "bmi for the penguin -- 220lbs, 3ft 3.2in:")
  print( "Expect: " + str(100) + " (approx)" )
  print( "Actual: " + str(bmi(220, 3, 3.2)) )
    

Your Task: Add a tst for your previous lab08. You can start with the sample shown above, but

• Add one more test for bmi; you can choose somebody who weighs 0lbs, if that makes things easier for you!
• Make at least three tests for middleThird:
  • What is the expected result for the middle of (the very-short story) "abc"?
  • What is the expected result for the middle of "abcdef"?
  • Make one longer test (length > 6); be sure to figure out what the middle third is by hand, before you run it!

home—info—labs—exams—hws
—D2L—MediaSamples/—breeze (snow day)—tutor/PIs

©2014, Ian Barland, Radford University Last modified 2014.Mar.31 (Mon)

Please mail any suggestions (incl. typos, broken links) to ibarlandradford.edu