CS 111
Summer 2 2018

Problem Set 1 FAQ

Problem Set 1 FAQ

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General questions

  1. I get an error message that mentions a TypeError when I add something to a list. What should I do?

    If you get something like the following error.

    TypeError: can only concatenate list (not "int") to list

    you are likely trying to add an integer to a list.

    Suppose you have two lists called xs and ys.

    x = [0, 1, 2]
    y = [3, 4, 5]

    And you would like to make a list that contains [0, 1, 2, 3]. You might try doing the following:

    x + y[0]

    Unfortunately, this is not allowed in Python, because addition between a list and an integer is not defined. If you think about it, this makes sense: how would you add a list to an integer? Instead, recall that the + operator can be used to concatenate two lists. Knowing this, we can put y[0] inside its own list and concatenate that with the list x.

    x + [y[0]]