Re: [Tutor] about assert
--- [EMAIL PROTECTED] wrote: > >>Python manual has a very brief introduction > >>of "assert" statements. It is very difficult > > First you probably don't need to use asserts > very often, they are useful if you are building > production strength code but for most users > of Python the exception mechanism is good enough. > This link makes some good points about how and when to use assertions: http://java.sun.com/j2se/1.4.2/docs/guide/lang/assert.html __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] about assert
>>Python manual has a very brief introduction >>of "assert" statements. It is very difficult First you probably don't need to use asserts very often, they are useful if you are building production strength code but for most users of Python the exception mechanism is good enough. Basically we use asserts to check pre and post conditions as well as\ invariants in functions. Anything other than that should be done using explicit if/else or exceptions. The reason for that is that asserts only operate when the code is in debug mode... so they should not be used for normal run time error detection. Typical things to check are that input values are within expected ranges and of desired types. Also that the final retrurn value of a function is within expected limits. Once we finish testing the overhead of those checks might not be required in the final version if we are sure they will never deviate from the test results. The syntax can be demonstrated quite easily and Luke has done that, the intent is a little less obvious and IMHO really needs a larger example to make the value obvious. Since I'm at a cyber-cafe net terminal I dont feel like trying that just now! :-) HTH, Alan G. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] about assert
--- "linda.s" <[EMAIL PROTECTED]> wrote: > Python manual has a very brief introduction of > "assert" statements. It > is very difficult for me to understand it. Every program has some fundamental assumptions that must remain true in order for the program to continue giving correct results. The assert statement is used to verify those assumptions. (The optional 2nd parameter can be used to give additional information about what went wrong.) For example, in my world no one is allowed to have a negative age. A negative age means my program is hopelessly confused and should halt immediately. >>> myAge=42 >>> assert myAge>=0 ## this is OK >>> myAge= -1## logically impossible >>> assert myAge >= 0 Traceback (most recent call last): File "", line 1, in ? AssertionError ## here I print the condition that failed >>> assert myAge >=0, 'myAge >= 0' Traceback (most recent call last): File "", line 1, in ? AssertionError: myAge >= 0 __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] about assert
linda.s wrote: > Python manual has a very brief introduction of "assert" statements. It > is very difficult for me to understand it. Can anyone give me an > example? > #example of assert.py def test(a): if 25 / 4 == a: return True else: return False def assert_it(a): try: assert a print "Success!" except AssertionError: print "something went wrong!" f = test(4) assert_it(f) f = test(6) assert_it(f) #--- end code It seems to me that you don't really need to know what assert is, because the value of __debug__ will probably be true, and so you might as well write if not a: raise AssertionError instead, except I guess assert is shorter. But then if you use assert assuming __debug__ will be true, then if it's not bad things will happen. I'm sure someone can give you a better explanation of this, but I have to get to class. HTH, -Luke > Thanks, > Linda > ___ > Tutor maillist - Tutor@python.org > http://mail.python.org/mailman/listinfo/tutor > > ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
