Python: Creating an empty file object

Question

I am attempting to make a logging module for Python that does not work because it fails on creation of the file object.

debug.py:

import os
import datetime
import globals

global fil
fil = None

def init(fname):
     fil = open(fname, 'w+')
     fil.write("# PyIDE Log for" + str(datetime.datetime.now()))

def log(strn):
    currentTime = datetime.datetime.now()

    fil.write(str(currentTime) + ' ' + str(os.getpid()) + ' ' + strn)
    print str(currentTime) + ' ' + str(os.getpid()) + ' ' + strn

def halt():
    fil.close()

fil will not work as None as I get an AttributeError. I also tried creating a dummy object:

fil = open("dummy.tmp","w+")

but the dummy.tmp file is written to instead, even though init() is called before log() is. Obviously you cannot open a new file over an already opened file. I attempted to close fil before init(), but Python said it could not perform write() on a closed file.

This is the code that is accessing debug.py

if os.path.exists(temp):
         os.rename(temp, os.path.join("logs","archived","log-" + str(os.path.getctime(temp)) + ".txt"))
         debug.init(globals.logPath)
         debug.log("Logger initialized!")

I would like to have logging in my program and I cannot find a workaround for this.

out of curiosity, why arent you encompassign this in a class? Im pretty sure you would avoid this issue if you did this in a class — TehTris
– TehTris, Commented May 19, 2015 at 20:06
@septi this won't work because I have a log archiving system set up. See the last code snippet. The file accesses conflict. If I open the file with debug.py before init() then I will not be able to wite because it is already used by a process. — Galen Nare
– Galen Nare, Commented May 19, 2015 at 20:08
its also possible hes just trying to learn how to do something on his own? its always good practice to implement something that already exists on your own. — TehTris
– TehTris, Commented May 19, 2015 at 20:18
It's always a good practice to learn some basic modules which are used in nearly every single project. — tamasgal
– tamasgal, Commented May 19, 2015 at 20:21

Open AI - Opting Out · Accepted Answer · 2015-05-19 20:09:51Z

6

Your problem is that you don't assign to the global fil:

def init(fname):
    fil = open(fname, 'w+')

This creates a new local variable called fil.

If you want to assign to the global variable fil you need to bring it into the local scope:

def init(fname):
    global fil
    fil = open(fname, 'w+')

answered May 19, 2015 at 20:09

Open AI - Opting Out

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2 Comments

Galen Nare Over a year ago

Thank you. I had learned that global could only be used outside of functions. I learned wrong.

tamasgal Over a year ago

And now learn to forget global at all and try to not use it ever again.

Community · Accepted Answer · 2017-05-23 12:09:45Z

If you want to MAKE your own logging module, then you may want to turn what you already have into a class, so you can import it as a module.

#LoggerThingie.py
import os
import datetime



class LoggerThingie(object):
    def __init__(self,fname):
         self.fil = open(fname, 'w+')
         self.fil.write("# PyIDE Log for" + str(datetime.datetime.now()))

    def log(self,strn):
        currentTime = datetime.datetime.now()
        self.fil.write(str(currentTime) + ' ' + str(os.getpid()) + ' ' + strn)
        print str(currentTime) + ' ' + str(os.getpid()) + ' ' + strn

    def halt(self):
        self.fil.close()

If you did this as a class, you would not have to keep track of globals in the first place (which is generally understood as bad practice in the world of programming: Why are global variables evil? )

Since it is now a module on its own, when you want to use it in another python program you would do this:

from LoggerThingie import LoggerThingie
#because module filename is LoggerThingie.py and ClassName is LoggerThingie

and then use it wherever you want, for example:

x = LoggerThingie('filename.txt') #create LoggerThingie object named x

and every-time you want to insert logs into it:

x.log('log this to the file')

and when you are finally done:

x.halt() # when ur done

Facundo Casco · Accepted Answer · 2015-05-19 20:29:42Z

0

If you don't want to start with an empty file you could use StringIO to keep the messages in memory and write them to disk at the end but be careful, if something happened and you didn't wrote the messages they will be lost.

edited May 19, 2015 at 20:29

answered May 19, 2015 at 20:09

Facundo Casco

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1 Comment

Galen Nare Over a year ago

Please look at the comments on the question.

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