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Python I/o Error


The except IOError: line catches the exception and executes your own block of code, which in this case just prints a more pleasant error message. Python Knowledge Base answers common questions about files. exception BaseException¶ The base class for all built-in exceptions. Getting rid of it made the print appear. this content

One may also instantiate an exception first before raising it and add any attributes to it as desired. >>> try: ... The mode attribute of a file object tells you in which mode the file was opened. See the discussion above for more information on exception instance attributes. The read method reads a specified number of bytes from the open file and returns a string with the data that was read. https://docs.python.org/2/library/exceptions.html

Python Exception Class

Fill in the Minesweeper clues Half the pentagon! It is a subclass of UnicodeError. Example: >>> x = 5 >>> y = 3 >>> assert x < y, "x has to be smaller than y" Traceback (most recent call last): File "", line 1, in Searching a list for a non-existent value will raise a ValueError exception.

  1. The Python Software Foundation is a non-profit corporation.
  2. Since you haven't done anything with this file yet, the current position is 0, which is the beginning of the file.
  3. exception NotImplementedError¶ This exception is derived from RuntimeError.
  4. This can be raised directly by codecs.lookup().
  5. For example, err.object[err.start:err.end] gives the particular invalid input that the codec failed on.

Getting a password is accomplished differently on UNIX, Windows, and Mac OS platforms, but this code encapsulates all of those differences. share|improve this answer answered Oct 11 '13 at 14:00 Alexander L. This one-liner opens the file, reads its contents, and prints them. Python Custom Exception This could be the IOError exception raised by the call to open, seek, or read.

This must be either an exception instance or an exception class (a class that derives from Exception). Would you rather get back an unusable file object to a non-existent file? A call to sys.exit() is translated into an exception so that clean-up handlers (finally clauses of try statements) can be executed, and so that a debugger can execute Accessing a non-existent dictionary key will raise a KeyError exception.

exception PendingDeprecationWarning¶ Base class for warnings about features which will be deprecated in the future. Python Valueerror Example exception Warning¶ Base class for warning categories. This is called an unhandled exception. x = 1/0 ... >>> try: ...

Python 3 Exceptions

The following exceptions are used as warning categories; see the warnings module for more information. http://www.java2s.com/Code/Python/File/HandlingIOErrors.htm exception EnvironmentError¶ The base class for exceptions that can occur outside the Python system: IOError, OSError. Python Exception Class Exceptions¶ Even if a statement or expression is syntactically correct, it may cause an error when an attempt is made to execute it. Python Filenotfounderror There are two basic file modes: "Append" mode will add data to the end of the file. "write" mode will overwrite the file.

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 Main menu Skip to primary content news print "result is", result ... The exceptions are defined in the module exceptions. This replaces the default behavior of creating the args attribute. Python Exception Message

The TypeError raised by dividing two strings is not handled by the except clause and therefore re-raised after the finally clause has been executed. Was Sigmund Freud "deathly afraid" of the number 62? [email protected]:~/tmp$ else Clause The try ... have a peek at these guys New in version 1.5.2.

print "The file does not exist, exiting gracefully" ... Python Exception Class Methods python share|improve this question edited Oct 11 '13 at 14:08 asked Oct 11 '13 at 13:45 user220201 1,43342747 1 could you paste the output of your program? –tback Oct 11 The next example demonstrates how to use an exception to support platform-specific functionality.

Instances have an attribute code which is set to the proposed exit status or error message (defaulting to None).

More information on classes is presented in chapter Classes. 8.6. Closing Files 6.2.3. except statement has an optional else clause. Assertionerror Python Does the code terminate?

If you're opening a file, it might not exist. The error is caused by (or at least detected at) the token preceding the arrow: in the example, the error is detected at the keyword print, since a colon (check my blog share|improve this answer edited Oct 11 '13 at 14:26 answered Oct 11 '13 at 14:20 KobeJohn 3,74522035 add a comment| up vote 2 down vote Your first exception handler tries to

This is where you start to appreciate it.) The open function may raise an IOError. (Maybe the file doesn't exist.) The seek method may raise an IOError. (Maybe the file is finally) So far the try statement had always been paired with except clauses. executing finally clause >>> divide("2", "1") executing finally clause Traceback (most recent call last): File "", line 1, in File "", line 3, in divide TypeError: unsupported operand type(s) for finally: ...

There are (at least) two distinguishable kinds of errors: syntax errors and exceptions. 8.1. In real world applications, the finally clause is useful for releasing external resources (such as files or network connections), regardless of whether the use of the resource was successful. 8.7. Please donate. Instances of this class have attributes filename, lineno, offset and text for easier access to the details. str() of the exception instance returns only the message.

asked 3 years ago viewed 1188 times active 3 years ago Blog Stack Overflow Podcast #92 - The Guerilla Guide to Interviewing Visit Chat Related 2738How do I check whether a Not the answer you're looking for? This allows the exception to properly propagate up and cause the interpreter to exit. exception DeprecationWarning¶ Base class for warnings about deprecated features.

Errors and Exceptions¶ Until now error messages haven't been more than mentioned, but if you have tried out the examples you have probably seen some. That was no valid number. A word for acting in advance of some expected or anticipated outcome How do I install the latest OpenOffice? other minor things with function and variable names you can see where I have changed things in the code above.

Example6.6.File Objects in MP3FileInfo try: fsock = open(filename, "rb", 0) try: fsock.seek(-128, 2) tagdata = fsock.read(128) finally: fsock.close() . . . If no exception occurs during the execution, the execution will reach the break statement and the while loop will be left. exception TypeError¶ Raised when an operation or function is applied to an object of inappropriate type.