Conditional for...in failing with utf-8, Spanish book translation

[Hunter]

Hi all,

This is my first Usenet post!
I've run into a wall with my first Python program. I'm writing some 
simple code to take a text file that's utf-8 and in Spanish and to use 
online translation tools to convert it, word-by-word, into English. Then 
I'm generating a PDF with both of the languages.

Most of this is working great, but I get intermittent errors of the form:

---

Translating coche(coche)...
 Already cached!
 English: car
Translating ahora(ahora)...
 tw returned now
 English: now
Translating mismo?(mismo)...
 Already cached!
 English: same
Translating ¡A(�a)...
iconv: illegal input sequence at position 0
 tw returned error: the required parameter "srctext" is missing
 English: error: the required parameter "srctext" is missing

---

The output should look like:
Translating Raw_Text(lowercaserawtextwithoutpunctuation)...
 tw returned englishtranslation
 English: englishtranslation

I've narrowed the problem down to a simple test program. Check this out:

---

# -*- coding: utf-8 -*-

acceptable = "abcdefghijklmnopqrstuvwxyzóíñú" # this line will work
acceptable = "abcdefghijklmnopqrstuvwxyzóíñúá" # this line won't
#wtf?

word = "¡A"
word_key = ''.join([c for c in word.lower() if c in acceptable])
print "word_key = " + word_key

---

Any ideas? I'm really stumped!

Thanks,
Hunter