Python Exception Argument Error
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This module never needs to be imported explicitly: the exceptions are provided in the built-in namespace as well as the exceptions module. For class exceptions, in a try statement with an except clause
Python Exception Message
that mentions a particular class, that clause also handles any exception classes derived from python custom exception that class (but not exception classes from which it is derived). Two exception classes that are not related via subclassing are
Python Raise Valueerror
never equivalent, even if they have the same name. The built-in exceptions listed below can be generated by the interpreter or built-in functions. Except where mentioned, they have an "associated value" indicating the detailed python filenotfounderror cause of the error. This may be a string or a tuple containing several items of information (e.g., an error code and a string explaining the code). The associated value is the second argument to the raise statement. If the exception class is derived from the standard root class BaseException, the associated value is present as the exception instance's args attribute. User code can raise built-in exceptions. python exception stack trace This can be used to test an exception handler or to report an error condition "just like" the situation in which the interpreter raises the same exception; but beware that there is nothing to prevent user code from raising an inappropriate error. The built-in exception classes can be subclassed to define new exceptions; programmers are encouraged to derive new exceptions from the Exception class or one of its subclasses, and not from BaseException. More information on defining exceptions is available in the Python Tutorial under User-defined Exceptions. The following exceptions are only used as base classes for other exceptions. exception BaseException¶ The base class for all built-in exceptions. It is not meant to be directly inherited by user-defined classes (for that, use Exception). If str() or unicode() is called on an instance of this class, the representation of the argument(s) to the instance are returned, or the empty string when there were no arguments. New in version 2.5. args¶ The tuple of arguments given to the exception constructor. Some built-in exceptions (like IOError) expect a certain number of arguments and assign a special meaning to the elements of this tuple, while others are usually called only with a single string giving a
a try statement with an except clause that mentions a particular class, that
Python Exception Class Methods
clause also handles any exception classes derived from that class (but python errno not exception classes from which it is derived). Two exception classes that are not related
Python Attributeerror Object Has No Attribute
via subclassing are never equivalent, even if they have the same name. The built-in exceptions listed below can be generated by the interpreter or built-in functions. https://docs.python.org/2/library/exceptions.html Except where mentioned, they have an "associated value" indicating the detailed cause of the error. This may be a string or a tuple of several items of information (e.g., an error code and a string explaining the code). The associated value is usually passed as arguments to the exception class's constructor. User code https://docs.python.org/3/library/exceptions.html can raise built-in exceptions. This can be used to test an exception handler or to report an error condition "just like" the situation in which the interpreter raises the same exception; but beware that there is nothing to prevent user code from raising an inappropriate error. The built-in exception classes can be subclassed to define new exceptions; programmers are encouraged to derive new exceptions from the Exception class or one of its subclasses, and not from BaseException. More information on defining exceptions is available in the Python Tutorial under User-defined Exceptions. When raising (or re-raising) an exception in an except or finally clause __context__ is automatically set to the last exception caught; if the new exception is not handled the traceback that is eventually displayed will include the originating exception(s) and the final exception. When raising a new exception (rather than using a bare raise to re-raise the exceptio
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 parsing errors, are perhaps the most https://docs.python.org/2.7/tutorial/errors.html common kind of complaint you get while you are still learning Python: >>> while True print 'Hello world' File "
a little mini-tutorial for Python programmers, aboutexceptions… First, this isbad: try: some_code() except: revert_stuff() raise Exception("some_code failed!") It is bad because all the information about how some_code() failed is lost. The traceback, the error message itself. Maybe it was an expected error, maybe itwasn't. Here's a modest improvement (but still not verygood): try: some_code() except: import traceback traceback.print_exc() revert_stuff() raise Exception("some_code failed!") traceback.print_exc() prints the original traceback to stderr. Sometimes that's the best you can do, because you really want to recover from an unexpected error. But if you aren't recovering, this is what you shoulddo: try: some_code() except: revert_stuff() raise Using raise with no arguments re-raises the last exception. Sometimes people give a blank never use "except:" statement, but this particular form (except: + raise) isokay. There's another form of raise that not many people know about, but can also be handy. Like raise with no arguments, it can be used to keep thetraceback: try: some_code() except: import sys exc_info = sys.exc_info() maybe_raise(exc_info) def maybe_raise(exc_info): if for some reason this seems like it should be raised: raise exc_info[0], exc_info[1], exc_info[2] This can be handy if you need to handle the exception in some different part of the code from where the exception happened. But usually it's not that handy; it's an obscure feature for areason. Another case when people often clobber the traceback is when they want to add information to it,e.g.: for lineno, line in enumerate(file): try: process_line(line) except Exception, exc: raise Exception("Error in line %s: %s" % (lineno, exc)) You keep the error message here, but lose the traceback. There's a couple ways to keep that traceback. One I sometimes use is to retain the exception, but change themessage: except Exception, exc: args = exc.args if not args: arg0 = '' else: arg0 = args[0] arg0 += ' at line %s' % lineno exc.args = arg0 + args[1:] raise It's a little awkward. Technically (though