从列表中搜索元素列表

Question

I need some help with my code. I want to search for the element in the list of arrays when I use this:

program_button = [elem.control for elem in self.program_buttons]
positions_X = list()
positions_Y = list()
for elem in program_button:
    positions_X.append(elem.getX())
    positions_Y.append(elem.getY())
posX = map(str, positions_X)
posY = map(str, positions_Y)

print posX

Here is the results:

19:42:50 T:2264  NOTICE: ['25', '375', '723', '1073', '1771', '2120', '2469']

I want to search the element 723 from the list.

Can you please show me an example of how I can search the element 723 from the list using the variable called posX ?

Answer 1

Assuming you want to get the index of the element 723 in the list you can use :

posX.index('723')

The below convenient function can be used if the item happens to not be in the list :

def search_item(L,item):
    try:
        return L.index(item)
    except ValueError:
        return -1

Call it with print(search_item(posX,'723')) which will return 2 in your case.
If the element is not foundable, the function will return -1.

Answer 2

You can use a generator expression within next function :

>>> next((i for i in posX if i == '723'),None)
'723'

This will returns the variable you are searching if it exist or None if it doesn't.

And if you want to check the existence of this value you can just use in operand :

if `723` in Posx:
    #do stuff

And if you want to return the index you can use list.index method with a try-except statement for handling the ValueError or use enumerate within preceding script :

>>> next((i for i,j in enumerate(posX) if j == '723'),None)
2