Beginning Python - From Novice to Professional

246 CHAPTER 10 ■ BATTERIES INCLUDED
$ python find_sender.py message.eml
Foo Fie
You should note the following about this program:
• I compile the regular expression to make the processing more efficient.
• I enclose the subpattern I want to extract in parentheses, making it a group.
• I use a nongreedy pattern to match the name because I want to stop matching when I reach the first left
angle bracket (or, rather, the space preceding it).
• I use a dollar sign to indicate that I want the pattern to match the entire line, all the way to the end.
• I use an if statement to make sure that I did in fact match something before I try to extract the match
of a specific group.
To list all the e-mail addresses mentioned in the headers, you need to construct a regular expression that matches
an e-mail address but nothing else. You can then use the method findall to find all the occurrences in each line.
To avoid duplicates, you keep the addresses in a set (described earlier in this chapter). Finally, you extract the keys,
sort them, and print them out:
import fileinput, re
pat = re.compile(r'[a-z\-\.]+@[a-z\-\.]+', re.IGNORECASE)
addresses = set()
for line in fileinput.input():
for address in pat.findall(line):
addresses.add(address)
for address in sorted(addresses):
print address
The resulting output when running this program (with the preceding e-mail message as input) is as follows:
Mr.Gumby@bar.baz
foo@bar.baz
foo@baz.com
magnus@bozz.floop
Note that when sorting, uppercase letters come before lowercase letters.
■Note I haven’t adhered strictly to the problem specification here. The problem was to find the addresses
in the header, but in this case the program finds all the addresses in the entire file. To avoid that, you can
call fileinput.close() if you find an empty line because the header can’t contain empty lines, and you
would be finished. Alternatively, you can use fileinput.nextfile() to start processing the next file, if
there is more than one.