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 x and y.

   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]]
   

2. Do our functions need to have the exact names that you have specified in the assignment? What about the variables for the inputs?

   Your functions must have the exact names that we have specified, or we won’t be able to test them. Note in particular that the case of the letters matters, and that some of the function names have one or more underscore characters (e.g., larger_gap).

   For the variables specified for the inputs, you could in theory use different names, as long as they are still as descriptive as the original ones. However, when there are multiple inputs, you must keep the inputs in the same order that we specified in the assignment, or we won’t be able to test your function.

3. I’ve read about or used some Python functions that we have not discussed in lecture. Can I use them in the homework?

   No. You should solve the problems in the homework using only constructs that we have discussed in lecture or that you have seen in the textbook. In addition, some of the problems have specific instructions regarding which functions you should or should not use. There are, of course, many different ways to accomplish the homework assignments, but we construct the assignments so that you can solve them using the tools that we have learned about in class.

   As a reminder, you are prohibited from consulting with external sites such as Stack Overflow about the homework assignments, as well as from using ChatGPT or other generative AI tools when solving the homework problems. Please review our policies as needed.

4. Do we need to use recursion on this assignment?

   No. None of the functions that we’re asking you to write for this assignment require recursion. If you wrote one or more of them using recursion, that’s okay, too, but doing so is not required.

5. I think I’m done with the assignment. Are there any things I should check before I submit?

   1. Be sure all of your functions return values instead of printing them.
   2. Include a docstring in all of your functions.
   3. Be sure to run your code after you add your docstrings to ensure that it still runs. If it doesn’t, you may have introduced problems involving the indentation of your docstrings.

Problem 4

1. I’m not sure exactly what I need to do when tracing functions. Do you have any suggestions?

   We covered a similar tracing problem in lecture. That steps taken to solve that problem can also be seen in the pre-lecture video called Tracing Function Calls that can be found in the Blackboard folder for September 20’s lecture.

Problem 5

1. What should begins_with return if the specified prefix is a substring of the specified word, but isn’t actually at the beginning of the word?

   It should return False. The function should only return True if the specified word begins with the specified prefix. For example:

   >>> begins_with('compute', 'put')
   result: False
   
   >>> begins_with('compute', 'com')
   result: True
   

2. Does begins_with need to handle the case in which prefix is longer than word?

   Yes, and we’ve included an example for this case to the problem description:

   >>> begins_with('begin', 'bigger')
   result: False
   

Problem 6

2. How can I pad a string in Python?

   Remember that you can concatenate strings with the + operator just like you can concatenate lists. Therefore, if you have a variable called pad that represents the necessary padding, you can just concatenate it to the string.

   To create the necessary padding, recall that you can repeat a string by using the * operator. For example, if I wanted a string consisting of five a‘s, I could do the following:

   'a' * 5
   

Last updated on September 15, 2025.