Accessing a value in a tuple that is in a list

Question

[(1,2), (2,3), (4,5), (3,4), (6,7), (6,7), (3,8)] 

How do I return the 2nd value from each tuple inside this list?

Desired output:

[2, 3, 5, 4, 7, 7, 8] 

Answer 1

With a list comprehension.

[x[1] for x in L] 

Answer 2

Ignacio's answer is what you want. However, as someone also learning Python, let me try to dissect it for you... As mentioned, it is a list comprehension (covered in DiveIntoPython3, for example). Here are a few points:

[x[1] for x in L]

• Notice the []'s around the line of code. These are what define a list. This tells you that this code returns a list, so it's of the list type. Hence, this technique is called a "list comprehension."
• L is your original list. So you should define L = [(1,2),(2,3),(4,5),(3,4),(6,7),(6,7),(3,8)] prior to executing the above code.
• x is a variable that only exists in the comprehension - try to access x outside of the comprehension, or type type(x) after executing the above line and it will tell you NameError: name 'x' is not defined, whereas type(L) returns <class 'list'>.
• x[1] points to the second item in each of the tuples whereas x[0] would point to each of the first items.
• So this line of code literally reads "return the second item in a tuple for all tuples in list L."

It's tough to tell how much you attempted the problem prior to asking the question, but perhaps you just weren't familiar with comprehensions? I would spend some time reading through Chapter 3 of DiveIntoPython, or any resource on comprehensions. Good luck.