Differences between enumerate(fileinput.input(file)) and enumerate(file)

Question

I'm looking for some help with my code which is rigth below :

for file in file_name :
    if os.path.isfile(file):
        for line_number, line in enumerate(fileinput.input(file, inplace=1)):
            print file
            os.system("pause")
            if line_number ==1:
                line = line.replace('Object','#Object')
                sys.stdout.write(line)

I wanted to modify some previous extracted files in order to plot them with matplotlib. To do so, I remove some lines, comment some others.

My problem is the following :

• Using for line_number, line in enumerate(fileinput.input(file, inplace=1)): gives me only 4 out of 5 previous extracted files (when looking file_name list contains 5 references !)

• Using for line_number, line in enumerate(file): gives me the 5 previous extracted file, BUT I don't know how to make modifications using the same file without creating another one...

Did you have an idea on this issue? Is this a normal issue?

Answer 1

There a number of things that might help you.

Firstly file_name appears to be a list of file names. It might be better named file_names and then you could use file_name for each one. You have verified that this does hold 5 entries.

The enumerate() function is used to help when enumerating a list of items to provide both an index and the item for each loop. This saves you having to use a separate counter variable, e.g.

for index, item in enumerate(["item1", "item2", "item3"]):
    print index, item

would print:

0  item1
1  item2
2  item3

This is not really required, as you have chosen to use the fileinput library. This is designed to take a list of files and iterate over all of the lines in all of the files in one single loop. As such you need to tweak your approach a bit, assuming your list of files is called file_names then you write something as follows:

# Keep only files in the file list
file_names = [file_name for file_name in file_names if os.path.isfile(file_name)]

# Iterate all lines in all files
for line in fileinput.input(file_names, inplace=1):
    if fileinput.filelineno() == 1:
        line = line.replace('Object','#Object')
        sys.stdout.write(line)  

The main point here being that it is better to pre filter any non-filenames before passing the list to fileinput. I will leave it up to you to fix the output.

fileinput provides a number of functions to help you figure out which file or line number is currently being processed.