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Python File Error Checking


Most exceptions are not handled by programs, however, and result in error messages as shown here: >>> 10 * (1/0) Traceback (most recent call last): File "", line 1, in Not the answer you're looking for? try-except-finally has been unified: try: non_existing_var except: print 'error' finally: print 'finished' share|improve this answer answered Dec 17 '08 at 15:05 Oli 7,35042033 Thanks, but I already knew about Or it could be locked, or not have read permission, or be some type of object that you can't read (like a directory), or be archived on tape and the tape this content

pass Note that the parentheses around this tuple are required, because except ValueError, e: was the syntax used for what is normally written as except ValueError But the file doesn't exist, so this raises the IOError exception. The only way I can think of is to use just except, which I usually don't want. If you know a line of code may raise an exception, you should handle the exception using a try...except block.

Python Exception Message

The first is that everyone can in the end, get what he wants, if he only tries. A common use in the standard Python library is to try to import a module, and then check whether it worked. This must be either an exception instance or an exception class (a class that derives from Exception). Once an exception has been handled, processing continues normally on the first line after the try...except block.

Baking at a lower temperature than the recipe calls for Human vs apes: What advantages do humans have over apes? raise NameError('HiThere') ... For example: >>> class MyError(Exception): ... Python Try Except Else After having printed the text of the print statement, the execution does another loop.

x = int(raw_input("Please enter a number: ")) ... Previous Chapter: Generators Next Chapter: Object Oriented Programming © 2011 - 2016, Bernd Klein, Bodenseo; Design by Denise Mitchinson adapted for python-course.eu by Bernd Klein Found a bug? http://stackoverflow.com/questions/5627425/what-is-a-good-way-to-handle-exceptions-when-trying-to-read-a-file-in-python Local VariablesFile ManagementModular Programming and ModulesIntroduction in Regular ExpressionsRegular Expressions, AdvancedLambda Operator, Filter, Reduce and MapList ComprehensionGeneratorsException HandlingObject Oriented ProgrammingInheritance ExampleSlotsClasses and Class CreationRoad to MetaclassesMetaclassesMetaclass Example: Count Function Calls Exception

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 Is Nested Try Block Possible In Python You can also provide a generic except clause, which handles any exception. Once again, if this import fails, Python will raise an ImportError, which you catch. Last updated on Sep 30, 2016.

  1. Related 2738How do I check whether a file exists using Python?3225What is a metaclass in Python?1587What is the difference between @staticmethod and @classmethod in Python?291Best practice for Python Assert259Python: check if
  2. def __init__(self, value): ...
  3. Even with some sleep in between. –Vivek May 26 '12 at 6:34 Added new link.
  4. You don't need to know or care which platform your code is running on -- just call getpass, and it will always do the right thing.
  5. What kind of bugs do "goto" statements lead to?
  6. What is summer in Spanish? "Estío" vs "verano" Words that are anagrams of themselves Prove sets equality.
  7. This gives false positives.
  8. If no exception occurs during the execution, the execution will reach the break statement and the while loop will be left.
  9. So the answer is either: "Tim's way" or "No, you're doing it correctly.".

Python Raise Custom Exception

There are reasons the read() could fail. see it here except NameError: ... Python Exception Message How does break enchantment work on stone shaped wall? Syntax For Generic Except Clause In Python First, the try clause (the statement(s) between the try and except keywords) is executed.

or was it more a grammatical use of the term where it is a return ? news Also see the comments to @Josh's proposal, which at least gets the syntax right. –delnan Apr 11 '11 at 21:17 Not seeing the problem. Exception classes can be defined which do anything any other class can do, but are usually kept simple, often only offering a number of attributes that allow information about the error Defining Clean-up Actions 8.7. Python Print Exception

The Python Software Foundation is a non-profit corporation. up vote 4 down vote favorite 1 I have the following code (adapted from an example given in Dive Into Python) that reads the entire contents of a file into a Exception classes can be defined which do anything any other class can do, but are usually kept simple, often only offering a number of attributes that allow information about the error have a peek at these guys Changing the print line to print("({0})".format(e)) fixed it. –matt wilkie Mar 15 '11 at 17:10 with no file i get ([Errno 2] No such file or directory: 'whatever.txt') with

Next number in sequence, understand the 1st mistake to avoid the 2nd Why is AT&T's stock price declining, during the days that they announced the acquisition of Time Warner inc.? Name Of Errors In Python OverflowError Raised when a calculation exceeds maximum limit for a numeric type. Most exceptions are not handled by programs, however, and result in error messages as shown here: >>> 10 * (1/0) Traceback (most recent call last): File "", line 1, in

Java and C++ use try...catch to handle exceptions, and throw to generate them.

If there are some other preconditions (e.g. share|improve this answer edited Sep 18 '14 at 4:39 community wiki 2 revs, 2 users 67%aitchnyu add a comment| up vote 6 down vote Testing for files and folders with os.path.isfile(), Errors and Exceptions 8.1. An Exception Can Be In Python has the same meaning: assert , The line above can be "read" as: If evaluates to False, an exception is raised and will be output.

share|improve this answer edited Dec 30 '15 at 14:59 Community♦ 11 answered Sep 17 '08 at 12:57 PierreBdR 20.4k83155 101 Unlike isfile(), exists() will yield True for directories. –Bulwersator Nov Was Sigmund Freud "deathly afraid" of the number 62? If I add an except block, under what conditions will it be executed, and how do I write a test to make sure it runs under those conditions? check my blog But whereas in Java exceptions are caught by catch clauses, we have statements introduced by an "except" keyword in Python.

For reference also see How to check whether a file exists using Python? Additionally, multiple patterns can be specified by splitting patterns with a ';' For example: >>> find('pox*', root='..') ['/Users/foo/pox/pox', '/Users/foo/pox/scripts/pox_launcher.py'] >>> find('*shutils*;*init*') ['/Users/foo/pox/pox/shutils.py', '/Users/foo/pox/pox/__init__.py'] >>> The implementation, if you care to look, An exception doesn't need result in a complete program crash, though. Try this.

Use this with extreme caution, since it is easy to mask a real programming error in this way! It's possible for a file to exist but for you to not be able to open it. It is useful for code that must be executed if the try clause does not raise an exception. Then when you call the getpass function, you're really calling a platform-specific function that this code has set up for you.

What does "they are facing their chest and shoulder" mean in this paragraph? IOErrorIOError Raised when an input/ output operation fails, such as the print statement or the open() function when trying to open a file that does not exist.Raised for operating system-related errors. result = x / y ... It can also be used to print an error message and then re-raise the exception (allowing a caller to handle the exception as well): import sys try: f = open('myfile.txt') s

Built-in Exceptions lists the built-in exceptions and their meanings. 8.3. SRC: http://www.pfinn.net/python-check-if-file-exists.html share|improve this answer edited Jul 18 '15 at 17:41 answered Apr 28 '15 at 2:45 Pedro Lobito 27.8k760111 The OP asked how to check if a file this_fails() ... In the IDE, that's no big deal, but if that happened while your actual Python program was running, the entire program would come to a screeching halt.