Python Invalid Arguments Error
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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 what is the argument of an exception in python quiz more about Stack Overflow the company Business Learn more about hiring developers or posting python valueerror example ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack python raise typeerror Overflow is a community of 6.2 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up How does one indicate invalid arguments in Python? [duplicate] up vote
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8 down vote favorite Possible Duplicate: python: Should I use ValueError or create my own subclass to handle invalid strings? Reading Built-in Exceptions I read: All user-defined exceptions should also be derived from this class" with regards to Exception. I also see a ValueError which says: Raised when a built-in operation or function receives an argument that has the right type but an inappropriate value, and the situation python exception get message is not described by a more precise exception such as IndexError. If I want to raise an exception for invalid arguments (the equivalent of Ruby's ArgumentError), what should I do? Should I raise ValueError directly, or preferably subclass ValueError with my own intention revealing name? In my case, I accept a key argument, but I want to restrict the set of characters in the key, such that only /\A[\w.]+\Z/ (Perl/Ruby regular expression) is accepted. python exception share|improve this question asked Feb 25 '11 at 2:39 Francois Beausoleil 8,95484264 marked as duplicate by Zooba, Francois Beausoleil, Jochen Ritzel, Chris Lutz, Josh Lee Feb 25 '11 at 2:58 This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question. add a comment| 2 Answers 2 active oldest votes up vote 6 down vote accepted I think the general idea is this: ValueError should almost always denote some sort of client error (where 'client' means the programmer using your interface). There are two high-level types of exceptions in Python: uncommon cases for otherwise normally functioning code; the client is not to blame usage errors where some interface is used incorrectly, or the
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Error Message Indicates In Python
Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping each other. Join them; it http://stackoverflow.com/questions/5113014/how-does-one-indicate-invalid-arguments-in-python only takes a minute: Sign up Invalid argument raise exception up vote 0 down vote favorite How do I test my parameter if it will raise an exception without actually raising it, using try and except? class MyClass: def function(parameter): pass parameter is an ambiguous function that may raise 1 or more of any exception, for example: parameter = pow("5", http://stackoverflow.com/questions/9026675/invalid-argument-raise-exception 5) A TypeError is raised as soon as the function is called and before the function can execute its statements. python class exception parameters share|improve this question edited Jan 26 '12 at 23:53 asked Jan 26 '12 at 22:52 Christopher Markieta 1,37852446 Why don't you want to use try ... except? Just for curiosity or is there any other reason? –Praveen Gollakota Jan 26 '12 at 23:00 Sorry if I was unclear, I do want to use try and except, but I don't know how it would work in the parameters. –Christopher Markieta Jan 26 '12 at 23:02 What your parameter will raise depends on how your function is implemented. In your example I don't see how parameter could raise an exception inside function. –Rik Poggi Jan 26 '12 at 23:06 If parameter is invalid it will raise an exception as soon as it is called. I want to be able to "catch" the exception with try and except. I do not have any information on what parameter will be exce
a try statement with an except clause that mentions a particular class, that clause also handles any exception classes derived from that class https://docs.python.org/3/library/exceptions.html (but not exception classes from which it is derived). Two exception classes that https://docs.python.org/2/library/argparse.html are not related 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. Except where mentioned, they have an "associated value" indicating the detailed cause of the error. This may be a string or in python 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 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 python invalid arguments 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 exception currently being handled), the implicit exception context can be supplemented with an explicit cause by using from with raise: raise new_exc from original_exc The expression following from must be an exception or None. It will be set as __cause__ on the raised exception. Setting __cause__ also implicitly sets the __suppress_context__ attribute to True
arguments and sub-commands¶ New in version 2.7. Source code: Lib/argparse.py Tutorial This page contains the API reference information. For a more gentle introduction to Python command-line parsing, have a look at the argparse tutorial. The argparse module makes it easy to write user-friendly command-line interfaces. The program defines what arguments it requires, and argparse will figure out how to parse those out of sys.argv. The argparse module also automatically generates help and usage messages and issues errors when users give the program invalid arguments. 15.4.1. Example¶ The following code is a Python program that takes a list of integers and produces either the sum or the max: import argparse parser = argparse.ArgumentParser(description='Process some integers.') parser.add_argument('integers', metavar='N', type=int, nargs='+', help='an integer for the accumulator') parser.add_argument('--sum', dest='accumulate', action='store_const', const=sum, default=max, help='sum the integers (default: find the max)') args = parser.parse_args() print args.accumulate(args.integers) Assuming the Python code above is saved into a file called prog.py, it can be run at the command line and provides useful help messages: $ python prog.py -h usage: prog.py [-h] [--sum] N [N ...] Process some integers. positional arguments: N an integer for the accumulator optional arguments: -h, --help show this help message and exit --sum sum the integers (default: find the max) When run with the appropriate arguments, it prints either the sum or the max of the command-line integers: $ python prog.py 1 2 3 4 4 $ python prog.py 1 2 3 4 --sum 10 If invalid arguments are passed in, it