Pythonic way to subtract one list from another with validation of presence
A good pythonic way to subtract one list from another is to use list comprehension: # remove all elements of list2 from list1 list1 = [x for x in list1 if x not in list2] How would I, in the same step, validate that each x actually occurs in list1 (e.g. in order to raise an error on missing elements)?
You don't need to check. x by definition has to be in list1, or else the iterator wouldn't provide it (since you're iterating over list1's items) But in case it might get modified while you're iterating (which is a case you should definitely avoid): list1 = [x for x in list1 if x not in list2 and x in list1] If you need more complex behaviour like showing an error message, use an explicit loop list_delta =  for x in list1: if x not in list1: raise IndexError("oh god what") if x not in list2: list_delta.append(x) But honestly this seems like an X-Y problem because you should never have to do this to begin with.
I'm not sure I understand what you're asking there, but if the order doesn't matter and there are no repetitions, you can use set difference as #Chih-Hsu Jack Lin mentioned in the comments: list(set(list1) - set(list2)) And if order doesn't matter, but element count does matter, another approach is to use collections.Counter: list((Counter(list1) - Counter(list2)).elements())
max-Function for attributes of objects
Parsing GET request data with from SimpleHTTPServer
Save Matplotlib image to s3 without saving locally using Boto
Adding attendees with Google Calendar API
matplotlib.pyplot issue with subplot, np.ones and np.arange?
Error When Trying to Run Simple Kivy Program (Windows)
Removing items for a list using a loop in Python
Tornado render() - Too many arguments
Plotting multiple points instead of just one in Python
AttributeError: 'NavigableString' object has no attribute 'find_all' (NameError)
Join mysql tables one after the other using python
Can two celery applications be interdependent? or two tasks of one application be interdependent?
How to insert map type into cassandra using cassandra-driver for python
How to deploy Django website in cPanel? [duplicate]
re.compile does not work properly
Using Appkit and Python to hide mouse cursor on OSX