Python Error Handling File Open
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you have probably seen some. There are (at least) two distinguishable kinds of errors: syntax errors and exceptions. 8.1. Syntax Errors¶ Syntax errors, also known as
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parsing errors, are perhaps the most common kind of complaint you get while python read file error handling you are still learning Python: >>> while True print('Hello world') File "
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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 look in case the input came from a script. 8.2. Exceptions¶ Even if a statement or expression is syntactically correct, it may
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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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Stack Overflow is a community of 6.2 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up What is python file exceptions 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 below. https://docs.python.org/3/tutorial/errors.html 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 1,05431621 add a comment| 4 Answers 4 active oldest votes up vote 6 down vote accepted http://stackoverflow.com/questions/5627425/what-is-a-good-way-to-handle-exceptions-when-trying-to-read-a-file-in-python 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 52.6k11103152 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(file): open(file)" method could
Python - Basic Syntax Python - Variable Types Python - Basic Operators Python - Decision Making Python - https://www.tutorialspoint.com/python/python_exceptions.htm Loops Python - Numbers Python - Strings Python - Lists http://www.diveintopython.net/file_handling/ Python - Tuples Python - Dictionary Python - Date & Time Python - Functions Python - Modules Python - Files I/O Python - Exceptions Python Advanced Tutorial Python - Classes/Objects Python - Reg Expressions Python - CGI Programming Python - Database error handling Access Python - Networking Python - Sending Email Python - Multithreading Python - XML Processing Python - GUI Programming Python - Further Extensions Python Useful Resources Python - Questions and Answers Python - Quick Guide Python - Tools/Utilities Python - Useful Resources Python - Discussion Selected Reading Developer's Best Practices Questions python error handling and Answers Effective Resume Writing HR Interview Questions Computer Glossary Who is Who Python Exceptions Handling Advertisements Previous Page Next Page Python provides two very important features to handle any unexpected error in your Python programs and to add debugging capabilities in them − Exception Handling: This would be covered in this tutorial. Here is a list standard Exceptions available in Python: Standard Exceptions. Assertions: This would be covered in Assertions in Python tutorial. List of Standard Exceptions − EXCEPTION NAME DESCRIPTION Exception Base class for all exceptions StopIteration Raised when the next() method of an iterator does not point to any object. SystemExit Raised by the sys.exit() function. StandardError Base class for all built-in exceptions except StopIteration and SystemExit. ArithmeticError Base class for all errors that occur for numeric calculation. OverflowError Raised when a calculation exceeds maximum limit for a numeric type. FloatingPointError Raised when a floating point calculat
Working with File Objects 6.2.1. Reading Files 6.2.2. Closing Files 6.2.3. Handling I/O Errors 6.2.4. Writing to Files 6.3. Iterating with for Loops 6.4. Using sys.modules 6.5. Working with Directories 6.6. Putting It All Together 6.7. Summary In this chapter, you will dive into exceptions, file objects, for loops, and the os and sys modules. If you've used exceptions in another programming language, you can skim the first section to get a sense of Python's syntax. Be sure to tune in again for file handling. 6.1.Handling Exceptions 6.1.1. Using Exceptions For Other Purposes Like many other programming languages, Python has exception handling via try...except blocks. Python uses try...except to handle exceptions and raise to generate them. Java and C++ use try...catch to handle exceptions, and throw to generate them. Exceptions are everywhere in Python. Virtually every module in the standard Python library uses them, and Python itself will raise them in a lot of different circumstances. You've already seen them repeatedly throughout this book. Accessing a non-existent dictionary key will raise a KeyError exception. Searching a list for a non-existent value will raise a ValueError exception. Calling a non-existent method will raise an AttributeError exception. Referencing a non-existent variable will raise a NameError exception. Mixing datatypes without coercion will raise a TypeError exception. In each of these cases, you were simply playing around in the Python IDE: an error occurred, the exception was printed (depending on your IDE, perhaps in an intentionally jarring shade of red), and that was that. This is called an unhandled exception. When the exception was raised, there was no code to explicitly notice it and deal with it, so it bubbled its way back to the default behavior built in to Python, which is to spit out some debugging information and give up. In the IDE, that's no big deal, but if that happened while your actual Python program was running