Error Trapping In Python
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you have probably seen some. There are (at least) two distinguishable kinds of errors: syntax errors and exceptions. 8.1. python error handling Syntax Errors¶ Syntax errors, also known as parsing errors, are perhaps
Python Catch All Errors
the most common kind of complaint you get while you are still learning Python: >>> while True print('Hello
Python Try Else
world') File "
Python 3 Exceptions
point in the line where the error was detected. The error is caused by (or at least detected at) the token preceding the arrow: in the example, the error is detected at the function print(), since a colon (':') is missing before it. File name and line number are printed so you know where to python custom exceptions look in case the input came from a script. 8.2. Exceptions¶ Even if a statement or expression is syntactically correct, it may cause an error when an attempt is made to execute it. Errors detected during execution are called exceptions and are not unconditionally fatal: you will soon learn how to handle them in Python programs. 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 "
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here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about hiring developers or posting ads with us http://stackoverflow.com/questions/5627425/what-is-a-good-way-to-handle-exceptions-when-trying-to-read-a-file-in-python Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community http://www.pythonforbeginners.com/error-handling/exception-handling-in-python Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up What is a good way to handle exceptions when trying to read a file in python? up vote 9 down vote favorite 2 I want to read a .csv file in python. I don't know if the file exists. My current solution is python exception below. It feels sloppy to me because the two separate exception tests are awkwardly juxtaposed. Is there 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 python file-io exception-handling share|improve this question edited Apr 11 '11 at 21:08 asked Apr 11 '11 at 20:51 CharlesHolbrow 1,04931521 add a comment| 4 Answers 4 active oldest votes up vote 6 down error trapping in vote accepted 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 share|improve this answer edited Apr 11 '11 at 21:23 answered Apr 11 '11 at 20:55 Josh Caswell 52.4k11103152 5 Just because a file exists doesn't mean that you can read it! –Gabe Apr 11 '11 at 20:59 1 This isn't perfect, because it is possible that the file gets deleted (e.g. by another process) between checking that it exists and trying to open it. –Liquid_Fire Apr 11 '11 at 20:59 1 It's also possible that fName could be the name of some file which, even if it sticks around, cannot be opened for whatever reason — for example, if it is a directory or does not have permissions allowing it to be read by the executing process. –intuited Apr 11 '11 at 21:14 1 The "if exists(f
with exceptions. What is an Exception? An exception is an error that happens during execution of a program. When that error occurs, Python generate an exception that can be handled, which avoids your program to crash. Why use Exceptions? Exceptions are convenient in many ways for handling errors and special conditions in a program. When you think that you have a code which can produce an error then you can use exception handling. Raising an Exception You can raise an exception in your own program by using the raise exception statement. Raising an exception breaks current code execution and returns the exception back until it is handled. Exception Errors Below is some common exceptions errors in Python: IOError If the file cannot be opened. ImportError If python cannot find the module ValueError Raised when a built-in operation or function receives an argument that has the right type but an inappropriate value KeyboardInterrupt Raised when the user hits the interrupt key (normally Control-C or Delete) EOFError Raised when one of the built-in functions (input() or raw_input()) hits an end-of-file condition (EOF) without reading any data Exception Errors Examples Now, when we know what some of the exception errors means, let's see some examples: except IOError: print('An error occurred trying to read the file.') except ValueError: print('Non-numeric data found in the file.') except ImportError: print "NO module found" except EOFError: print('Why did you do an EOF on me?') except KeyboardInterrupt: print('You cancelled the operation.') except: print('An error occurred.') Try to use as few try blocks as possible and try to distinguish the failure conditions by the kinds of exceptions they throw. Set up exception handling blocks To use exception handling in Python, you fir