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Trying to simplify lots of repetitive reading and writing in a script of mine, and I can not figure out how to get data out of def readfile.

def writefile(FILE, DATA):
    file = open(FILE, "w")
    X = str(DATA) 
    file.write(X)
    file.close()


def readfile(FILE):
    file = open(FILE, "r")
    readvar = file.read()
    file.close()


readfile("BAL.txt")
print(readvar)

I would expect the value stored in BAL.txt to come back, but it always says that readvar is not defined. I just defined it in a function that I ran.

Error:

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-6-f80fb5b2da05> in <module>
     14 
     15 readfile("test.txt")
---> 16 print(readvar)

NameError: name 'readvar' is not defined
Trenton McKinney
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  • Useful reading: [Python Scopes and Namespaces](https://docs.python.org/3/tutorial/classes.html#python-scopes-and-namespaces) – Patrick Haugh Jan 22 '18 at 22:42

3 Answers3

3
  • In Python, variables from inside a function are generally not accessible from the outside (Look up variable scoping).
  • You can put a return statement at the end of a function to return variables (readvar in this case) (and you almost always should).
  • Then you can assign the returned argument (readvar) to a new variable (e.g. rv).
  • You can also give it the same name.
  • Other Resources: 
def writefile(FILE, DATA):
    file = open(FILE, "w")
    X = str(DATA) 
    file.write(X)
    file.close()
    
    
def readfile(FILE):
    file = open(FILE, "r")
    readvar = file.read()
    file.close()
    return readvar


rv = readfile("BAL.txt")
print(rv)
Trenton McKinney
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Joooeey
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  • And you should use the `with` statement whenever you deal with files because it handles program crashes better. https://docs.python.org/3/tutorial/inputoutput.html#reading-and-writing-files – Joooeey Jan 22 '18 at 22:50
  • Thank you this will make this a lot easier to write –  Jan 22 '18 at 22:56
1

You're unable to see the value of readvar because it's only locally defined within the scope of the readfile function, not globally, as you're attempting to use it when calling print(readvar).

If you need a value to persist outside the scope of the function, you must return it to where the function is called, like so: 

def readfile(FILE):
    file = open(FILE, "r")
    file_data = file.read()
    file.close()
    return file_data

file_data = readfile("my_file.txt")
print(file_data)

I'd also suggest using a with block when performing file operations. It's best practice as to ensure the file handle is correctly closed, even if exceptions occur. This improves the handling of any errors the operation may encounter. For example: 

def writefile(FILE, DATA):
    data = str(DATA) 

    with open(FILE, 'w') as write_stream:
        write_stream.write(data)

def readfile(FILE):
    with open(FILE, 'r') as read_stream:
        file_data = read_stream.read()

    return file_data

file_data = readfile("my_file.txt")
print(file_data)

If you wanted to access the file line-by-line, we simply include a for loop within the scope of with. For example, printing each line of the file:

def readfile(FILE):
    with open(FILE, 'r') as read_stream:
        for line in read_stream
            print(line)
cognophile
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1

simple. try this one

def personal_data():

name1 = input("What is you 1st Name?").upper()
name2 = input("What is your last Name?").upper()
return name1 + name2

fname = personal_data()

print(fname)

Jhonie San Juan
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