Question

I am using Python 3.0 to write a program. In this program I deal a lot with lists which I haven’t used very much in Python.

I am trying to write several if statements about these lists, and I would like to know how to look at just a specific value in the list. I also would like to be informed of how one would find the placement of a value in the list and input that in an if statement.

Here is some code to better explain that:

count = list.count(1)
if count > 1
    (This is where I would like to have it look at where the 1 is that the count is finding)

Thank You!

Answer 1

First off, I would strongly suggest reading through a beginner’s tutorial on lists and other data structures in Python: I would recommend starting with Chapter 3 of Dive Into Python, which goes through the native data structures in a good amount of detail.

To find the position of an item in a list, you have two main options, both using the index method. First off, checking beforehand:

numbers = [2, 3, 17, 1, 42]
if 1 in numbers:
    index = numbers.index(1)
    # Do something interesting

Your other option is to catch the ValueError thrown by index:

numbers = [2, 3, 17, 1, 42]
try:
    index = numbers.index(1)
except ValueError:
    # The number isn't here
    pass
else:
    # Do something interesting

One word of caution: avoid naming your lists list: quite aside from not being very informative, it’ll shadow Python’s native definition of list as a type, and probably cause you some very painful headaches later on.