Accessing global file in the user defined function

Question

I am trying to access file which is opened globally as below:

with open("number.txt") as num:

    val=int(num.read())

consider

number.txt

will be having some number
After the above lines of code if I use the above file pointer inside a method as below:

def updateval():

    global num

    num.write(numb)

I am getting error as :

ValueError: I/O operation on closed file

If I open file inside function then there wont be any issue.But I want to open file only once so in many opther function I can perform file operation without opening again and again

Please help me in resolving this!!
Many thanks in advance..

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Answer 1

You have two problems:

with closes the file when the enclosing code block exists.
You open the file for reading, so even if you don't close the file, you can't write to it.

Solution 1:

with open('number.txt') as num:  # opens for read-only by default
    val = int(num.read())
# file is closed here

def updateval(numb):
    with output('number.txt','w') as num:  # re-opened for writing
        num.write(numb)
    # file is closed here

Solution 2 (if you really want to open the file once):

num = open('number.txt','r+')
val = int(num.read())

def updateval(numb):
    # You don't need "global" when you mutate an object,
    # only for new assignment, e.g. num = open(...)
    num.seek(0)           # make sure to write at the beginning of the file.
    num.truncate()        # erase the current content.
    num.write(str(numb))  # write the number as a string
    num.flush()           # make sure to flush it to disk.

Obviously, the second solution you have to micromanage what you are doing. Use solution 1.

Accessing global file in the user defined function

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