newbie question: for loop within for loop confusion

[Thomas Hill]

On Jun 15, 6:23 pm, takayuki <lawtonp... at gmail.com> wrote:
> def hasnolet(avoid):
>         fin = open('animals.txt')
>         for line in fin:
>                 word = line.strip()
>                 for letter in avoid:
>                         if letter in word:
>                                 break
>                         else:
>                                 print word

You're using the split command correctly, but you're not filtering
correctly. Consider this:

---begin---
fin = open('animals.txt')
"\n".join(["%s" % line for line in fin if len(line.strip('abcd')) ==
len(line)])
----end----

Let's go slow.

"\n".join([...])

1. Take everything that is in the following list, and print each one
with a carriage return appended to it.

"\n".join(["%s" % line for line in fin ...])

2. For each line in fin, create a string that only consists of what
currently in the line variable, using string substitution.

"\n".join(["%s" % line for line in fin if len(line.strip('abcd')) ==
len(line)])

3. Only do #2 if the length of the line after stripping out the
unnecessary characters is the same length as the line originally. This
way we filter out the lines we don't want. If we wanted the lines that
have been filtered, we can change "==" to "!=" or "<=".

Now, I read "Dive Into Python" first, which through these early on in
the book. If your eyes cross looking at this, write it down and read
it again after you get a little farther into the book you're reading