How to redirect stdout to only the console when within fileinput loop

Question

Currently I have this piece of code for python 2.7:

h = 0
for line in fileinput.input('HISTORY',inplace=1):
    if line[0:2] == x:
            h = h + 1
            if h in AU:
                    line = line.replace(x,'AU')
    if 'timestep' in line:
        h = 0
        sys.stdout.write(('\r%s%% ') % format(((os.stat('HISTORY').st_size / os.stat('HISTORY.bak').st_size)*100),'.1f'))
    sys.stdout.write(line)

What I am having trouble with is the following line:

sys.stdout.write(('\r%s%% ') % format(((os.stat('HISTORY').st_size / os.stat('HISTORY.bak').st_size)*100),'.1f'))

I need this information to be outputted to the console ONLY and not into the HISTORY file.

According to the fileinput documentation Optional in-place filtering: if the keyword argument inplace=1 is passed to fileinput.input() or to the FileInput constructor, the file is moved to a backup file and standard output is directed to the input file. Maybe removing inplace=1 is what you want? — cod3monk3y
– cod3monk3y, Commented Nov 13, 2014 at 19:37
That would work, but I need information from the backup file itself (i.e. HISTORY.bak) — kalk2
– kalk2, Commented Nov 13, 2014 at 19:47
Specifying inplace=1 will direct any stdout to the 'HISTORY' file, this includes print and sys.stdout.write. If you don't want to write to 'HISTORY' you'll have to remove inplace=1. You'll still be reading from that file. And you don't need it of you don't plan on writing back to it. — cod3monk3y
– cod3monk3y, Commented Nov 13, 2014 at 19:52
and 'sys.stdout.write(line)' needs to be written into the input file — kalk2
– kalk2, Commented Nov 13, 2014 at 19:52
Ah, okay! Since fileinput is just creating a temporary backup file when you use inplace=1, how about just creating a backup yourself, removing inplace=1, then re-creating the HISTORY file? sys.stdout.write(line) would be come f.write(line) and you could leave the other one in place? I'll post some code in an answer. — cod3monk3y
– cod3monk3y, Commented Nov 13, 2014 at 19:55

Community · Accepted Answer · 2017-05-23 12:05:58Z

1

This code creates a temporary copy of the input file, then scans this and rewrites the original file. It handles errors during processing the file so that the original data isn't lost during the re-write. It demonstrates how to write some data to stdout occasionally and other data back to the original file.

The temporary file creation was taken from this SO answer.

import fileinput
import os, shutil, tempfile

# create a copy of the source file into a system specified
# temporary directory. You could just put this in the original
# folder, if you wanted
def create_temp_copy(src_filename):
    temp_dir = tempfile.gettempdir()
    temp_path = os.path.join(temp_dir, 'temp-history.txt')
    shutil.copy2(src_filename,temp_path)
    return temp_path

# create a temporary copy of the input file
temp = create_temp_copy('HISTORY.txt')

# open up the input file for writing
dst = open('HISTORY.txt','w+')

for line in fileinput.input(temp):

    # Added a try/catch to handle errors during processing.
    # If this isn't present, any exceptions that are raised
    # during processing could cause unrecoverable loss of
    # the HISTORY file
    try:
        # some sort of replacement 
        if line.startswith('e'):
            line = line.strip() + '@\n' # notice the newline here

        # occasional status updates to stdout
        if '0' in line:
            print 'info:',line.strip() # notice the removal of the newline
    except:
        # when a problem occurs, just output a message
        print 'Error processing input file'

    finally:
        # re-write the original input file
        # even if there are exceptions
        dst.write(line)

# deletes the temporary file
os.remove(temp)

# close the original file
dst.close()

edited May 23, 2017 at 12:05

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answered Nov 13, 2014 at 20:28

cod3monk3y

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1 Comment

cod3monk3y Over a year ago

Glad to help. Also, checkout this variation on creating the temporary copy, which returns a file-like object which is automatically deleted on close. That code will allow you to get rid of fileinput.input and os.remove.

ACV · Accepted Answer · 2014-11-13 19:35:36Z

0

If you only want the information to go to the console could you just use print instead?

answered Nov 13, 2014 at 19:35

ACV

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1 Comment

kalk2 Over a year ago

I have tried using print, that also outputs the information to the HISTORY file.

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