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.

Answer 1

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+')

Answer 2

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

Answer 3

如果你不想从一个空文件开始，你可以使用StringIO将消息保存在内存中，并在最后将它们写入磁盘，但要小心，如果发生了什么事情并且你没有写入消息，它们就会丢失。