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220 CHAPTER 10 ■ BATTERIES INCLUDED
The function fileinput.filelineno returns the number of the current line within the current
file. Each time you are finished with one file and begin processing the next, the file line number
is reset, and restarts at 1.
The function fileinput.isfirstline returns a true value if the current line is the first line
of the current file—and a false value otherwise.
The function fileinput.isstdin returns a true value if the current file is sys.stdin and
false otherwise.
The function fileinput.nextfile closes the current file and skips to the next one. The
lines you skip do not count against the line count. This can be useful if you know that you are
finished with the current file—for example, if each file contains words in sorted order, and you
are looking for a specific word. If you have passed the word’s position in the sorted order, you
can safely skip to the next file.
The function fileinput.close closes the entire chain of files and finishes the iteration.
Example
Numbering the lines of a Python script. Let’s say you have written a Python script and you want to number the
lines. Because you want the program to keep working after you’ve done this, you have to add the line numbers in
comments to the right of each line. To line them up, you can use string formatting. Let’s allow each program line to
get 40 characters maximum and add the comment after that. The program in Listing 10-6 shows a simple way of
doing this with fileinput and the inplace parameter.
Listing 10-6. Adding Line Numbers to a Python Script
# numberlines.py
import fileinput
for line in fileinput.input(inplace=True):
line = line.rstrip()
num = fileinput.lineno()
print '%-40s # %2i' % (line, num)
If you run this program on itself, like this:
$ python numberlines.py numberlines.py
you end up with the program in Listing 10-7. Note that the program itself has been modified, and that if you run it
like this several times, you end up with multiple numbers on each line. Recall that rstrip is a string method that
returns a copy of a string, where all the whitespace on the right has been removed (see the section “String
Methods” in Chapter 3 and Table B-6 in Appendix B).