CODEWITHSUNDEEP
pythonerror-handling
Lishpee
Lishpee

Reputation: 21

How can I include file name error handling with this piece of code?

I am required to include some form of error handling when the user inputs the file name such that if they put a file name which is not within the programs directory then it will appear with an error message. This is the code at the moment:

board = [] 
fileinput = input("Please enter your text file name:")        
filename = fileinput + ".txt"   
file = open(filename, "r+")
for lines in file:
    board.append(list(map(int,lines.split())))

I'm not sure where to include the try/except as if I include it like this:

board = [] 
fileinput = input("Please enter your text file name:")        
filename = fileinput + ".txt"
try:
    file = open(filename, "r+")
    except:
        print("Error: File not found")
    for lines in file:
        board.append(list(map(int,lines.split())))

Then I get the following error:

line 28, in for lines in file: NameError: name 'file' is not defined

I know there probably is a very simple solution but I am struggling with wrapping my head around it.

Upvotes: 2

Views: 668

Answers (2)

fun4jimmy
fun4jimmy

Reputation: 751

To catch exceptions from the call to open only you can add an else clause to the end of the try ... except statement:

try:
    file = open(filename, "r+")
except:
    print("Error: File not found")
else:
    for lines in file:
        board.append(list(map(int,lines.split())))

From the https://docs.python.org/3/tutorial/errors.html documentation:

The try ... except statement has an optional else clause, which, when present, must follow all except clauses. It is useful for code that must be executed if the try clause does not raise an exception.

This ensures that we only catch errors from open and don't incorrectly report problems with the loop reading the file contents as the file was not found.

Catching all exception types using a bare except can also mean we incorrectly mask other errors as a missing file. It is always helpful to try and handle specific exception types (e.g. FileNotFoundError) so we can be specific in our error messages.

try:
    file = open(filename, "r+")
except FileNotFoundError:
    print("Error: File not found")
except OSError as error:
    print(f"Error: {error}")
else:
    for lines in file:
        board.append(list(map(int,lines.split())))

Additionally, so you don't forget to close the file you can use the with statement which you can also do this without wrapping the with block with a try except block:

try:
    file = open(filename, "r+")
except FileNotFoundError:
    print("Error: File not found")
except OSError as error:
    print(f"Error: {error}")
else:
    with file:
        for lines in file:
            board.append(list(map(int,lines.split())))

If you don't like that level of nesting, you could make the except clause return after printing an error but this depends on the flow of the rest of your program.

You may find logging.error is a useful replacement for print.

Upvotes: 0

Karls
Karls

Reputation: 751

You should include all lines which may occur error under try, so:

board = [] 
fileinput = input("Please enter your text file name:")        
filename = fileinput + ".txt"
try:
    file = open(filename, "r+")
    for lines in file:
        board.append(list(map(int,lines.split())))
except:
    print("Error: File not found")

The way you presented, the program try to ignore error and go over, which ends with NameError: name 'file' is not defined

The second problem in your case would be with scope - file is local variable in try and you call it outside of scope.

Upvotes: 1

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