Python -textual data(TypeError: unorderable types(str, float))

Head First Programming
A learner's guide to programming
using the Python language
( O'Reilly Media; )
David Griffiths (著) Paul Barry (著)

開発環境

• OS X Mavericks - Apple(OS)
• Emacs (CUI)、BBEdit - Bare Bones Software, Inc. (GUI) (Text Editor)
• Python (プログラミング言語)

Head First Programming A learner's guide to programming using the Python language (David Griffiths(著)、Paul Barry(著)、 O'Reilly Media; )のChapter 2(textual data: Every string has its place)、Code Magnets(p.61)を解いてみる。

Code Magnets(p.61)

コード(BBEdit)

sample61.py

#!/usr/bin/env python3
#-*- coding: utf-8 -*-

import urllib.request

price = 99.99
while price > 4.74:
    page = urllib.request.urlopen('http://beans-r-us.appspot.com/prices.html')
    text = page.read().decode('utf8')
    where = text.find('>$')
    start_of_price = where + 2
    end_of_price = where + 6
    price = text[start_of_price:end_of_price]

print('Buy!')

入出力結果(Terminal)

$ ./sample61.py
Traceback (most recent call last):
  File "./sample61.py", line 7, in <module>
    while price > 4.74:
TypeError: unorderable types: str() > float()
$