Python: While loop will not terminate

Question

I have read a lot of topics regarding while loops and I can't find one that tells me what I have done wrong with my own code. I am doing the Learn Python the Hard Way and I wrote this code in order to satisfy the study drill #1 for exercise 33. I cannot figure out why the loop won't terminate when I put in my raw data.

numbers = []
def number_uno(z):
 i = 0
 while i < z:
 print "At the top i is %d" % i
 numbers.append(i)
 i += 1
 print "Numbers now: ", numbers
 print "At the bottom i is %d" % i
print "Pick a random number: "
z = raw_input("> ")
number_uno(z)
print "Done"

Any ideas? it just keeps adding 1 to "i" and will not stop printing.

Thanks, Zach

Answer 1

raw_input returns a string. when you pass it to your function, you're comparing an integer and a string. Note that this behavior was deprecated in python3.x. You can't compare integers with strings in python 3.x in this way. (It'll raise a TypeError).

You can remedy this quite easily:

number_uno(int(z))

should run OK.

• Lev Levitsky: I wonder why it's even allowed in Python2 and what the result means.
• mgilson: @LevLevitsky -- in python2, the ordering is determined by object type, but is implementation dependent. In other words 1 > "foo" will give the same result as 100 > "bar", but what that result actually is isn't well defined.
• kindall: In CPython 2.x, the default behavior when comparing objects of different types is to compare their types as strings. Thus all integers are less than all strings, because "int" < "str". This was done to segregate the objects by type while sorting lists containing various types, but I don't believe other Python implementations are obliged to do the same.
• Lev Levitsky: Wow. I don't know what else to say :)
• mgilson: @kindall -- thanks for explaining the rational (and algorithm that cpython2.x uses). I always wondered how it decided since it's not mentioned in the docs