[python] What is a good way to handle exceptions when trying to read a file in python?

I want to read a .csv file in python.

  • I don't know if the file exists.
  • My current solution is below. It feels sloppy to me because the two separate exception tests are awkwardly juxtaposed.

Is there a prettier way to do it?

import csv    
fName = "aFile.csv"

try:
    with open(fName, 'rb') as f:
        reader = csv.reader(f)
        for row in reader:
            pass #do stuff here
    
except IOError:
    print "Could not read file:", fName

This question is related to python python-2.7 exception file-io

The answer is


fname = 'filenotfound.txt'
try:
    f = open(fname, 'rb')
except FileNotFoundError:
    print("file {} does not exist".format(fname))

file filenotfound.txt does not exist

exception FileNotFoundError Raised when a file or directory is requested but doesn’t exist. Corresponds to errno ENOENT.

https://docs.python.org/3/library/exceptions.html
This exception does not exist in Python 2.


Adding to @Josh's example;

fName = [FILE TO OPEN]
if os.path.exists(fName):
    with open(fName, 'rb') as f:
        #add you code to handle the file contents here.
elif IOError:
    print "Unable to open file: "+str(fName)

This way you can attempt to open the file, but if it doesn't exist (if it raises an IOError), alert the user!


I guess I misunderstood what was being asked. Re-re-reading, it looks like Tim's answer is what you want. Let me just add this, however: if you want to catch an exception from open, then open has to be wrapped in a try. If the call to open is in the header of a with, then the with has to be in a try to catch the exception. There's no way around that.

So the answer is either: "Tim's way" or "No, you're doing it correctly.".


Previous unhelpful answer to which all the comments refer:

import os

if os.path.exists(fName):
   with open(fName, 'rb') as f:
       try:
           # do stuff
       except : # whatever reader errors you care about
           # handle error


Here is a read/write example. The with statements insure the close() statement will be called by the file object regardless of whether an exception is thrown. http://effbot.org/zone/python-with-statement.htm

import sys

fIn = 'symbolsIn.csv'
fOut = 'symbolsOut.csv'

try:
   with open(fIn, 'r') as f:
      file_content = f.read()
      print "read file " + fIn
   if not file_content:
      print "no data in file " + fIn
      file_content = "name,phone,address\n"
   with open(fOut, 'w') as dest:
      dest.write(file_content)
      print "wrote file " + fOut
except IOError as e:
   print "I/O error({0}): {1}".format(e.errno, e.strerror)
except: #handle other exceptions such as attribute errors
   print "Unexpected error:", sys.exc_info()[0]
print "done"

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