how to express " if Not exist" concept in python

[kang jia]

hi, currently i am doing booking car online and one of the function is cancel and update booking. if the booking number users entered in is not exist. it will redirect the page stating that the booking number did not exist or you never book with us. however. i would like to express this "if Not exist" concept in my coding. how should i achieve this. the following is my code:

 
def deleteCar(request):
 
    if request.user.is_authenticated():
 
        Login = True
        myId=request.session['B_id']
        my = Booking1.objects.get(id= myId)
 
            IF NOT EXIST my:
                        return HttpResponseRedirect ("/nobooking/")
        else:
                        dateStr=my.booking_time
                now=datetime.datetime.now()
 
                print now
                one_day=60*60*24
                diff=comp_dates(dateStr,str(now).split('.')[0])
                print diff
 
        if diff > one_day:
            return HttpResponseRedirect ("/unable/")
 
        if diff < one_day:
            my.delete()
        else:
            return HttpResponseRedirect ("/Deny/")
 
    return render_to_response('confirmed_cancel.html')
 

the IF NOT EXIST is just my concept in the coding, can any one help me with code..thanks so much. ;)

[dazzler]

I'm not an expert and don't know what that Booking1.objects.get(id= myId) do , but can you search it first and check if it exist? In my code I have used sometimes try, expect in some places, it raises error if something doesn't exist (if for example trying to modify some variable that doesn't exist)

[kang jia]

I'm not an expert and don't know what that Booking1.objects.get(id= myId) do , but can you search it first and check if it exist? In my code I have used sometimes try, expect in some places, it raises error if something doesn't exist (if for example trying to modify some variable that doesn't exist)

i am using Django framework, Booking1.objects.get(id= myId) what this code do is the same as SQL select statement where id is equal to myId which is post over from previous page. yes, i have tried this if not exist phrase before i post this question in forum and it returns me invalid syntax. thanks for your kind reply as well.

[bvdet]

>>> obj = None
>>> print obj
None
>>> if not obj:
...     print "Object 'obj' evaluates to 'None'"
...     
Object 'obj' evaluates to 'None'
>>> obj = ""
>>> if not obj:
...     print "Object 'obj' evaluates to 'None'"
...     
Object 'obj' evaluates to 'None'
>>> obj = []
>>> if not obj:
...     print "Object 'obj' evaluates to 'None'"
...     
Object 'obj' evaluates to 'None'
>>> obj = {}
>>> if not obj:
...     print "Object 'obj' evaluates to 'None'"
...     
Object 'obj' evaluates to 'None'
>>> 

This is a very basic concept.