Question

This is a Doctor,Doctor it hurts when I do this question...but does anyone know why I get a "None" output when running from a module, and I don't get a "None" when I call a function from the Python Shell?

Answer 1

#As an exercise, write a function that takes a string as an
#argument and outputs the letters backward, one per line.

def spellBackwards(word):
loopCount=-1
while -1*loopCount<=len(word):
if word[loopCount]==None:
return " "
else:
print (word[loopCount])
loopCount-=1

print (spellBackwards("backwards"))

#I do get my backwards spelling, but at the end of that I get a "None". If I
#comment out the print statement "None" does not print. What is going on
#here? My if/else word[loopCount] apparently does nothing.

def spellBackwards1(word):
loopCount=1
while loopCount<=len(word):
print (word[len(word)-loopCount])
loopCount+=1
print (spellBackwards1("backwards"))

#this too gives me a "None" at the end.

def spellFrontwards(word):
loopCount=0
while loopCount<len(word):
print (word[loopCount])
loopCount+=1
print (spellFrontwards("frontwards"))

#but if the function is called from the shell I don't get the "None"

Answer 2

All functions return 'None' unless you use the keyword 'return to return something else. The shell suppresses the 'None' return. If you did some_var = spellFrontwards(word) and then print some_var it would show you the 'None'

Answer 3

Instead of using print at the end you could just type spellFrontwards("frontwards") ad your function already does the printing or you could make the function build up a variable with what you want to print and return it, then your last print would work as expected.

Answer 4

Thank You msmithhnova

Answer 5

Here's a recursive way to do it:

def reverse( string ):
if( len( string ) == 0 ):
return

char = string[ 0 ]
reverse( string[ 1: ] )
print char

if( __name__ == "__main__" ):
print reverse( "Hello World" )

Answer 6

Thanks rsmith6559,

that nice little program will help me think about recursion.