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‎pretext/functions/funcWithListsAndLoops.ptx‎

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</ul>
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</p>
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</introduction>
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<subsection xml:id="flal_list-indexing-and-slicing">
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<title>List Indexing and Slicing</title>
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<p>A list holds items in order and you can get the value at an index, just like you can with strings. You can also
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use negative indices, just like you can with strings. You can use the slice operator <c>[start:end]</c> with lists to get a
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new list by copying part of a list, just like you can with strings. The new list will include the item at the start index (inclusive) and
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all elements up to the end index - 1. </p>
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<exercise label="flal_neg_2_result">
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<statement>
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<p>What is the last thing that the following code prints?</p>
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<program language="python">
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<input>
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def list_get(lst):
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print(lst[0])
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print(lst[:2])
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return lst[-2]
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l = ["hi", 3, 'buy', 4]
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print(list_get(l))
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</input>
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</program>
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</statement>
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<choices>
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<choice>
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<statement>
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<p>hi</p>
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</statement>
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<feedback>
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<p>This would be true if it was returning the item at index 0 or -4.</p>
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</feedback>
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</choice>
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<choice>
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<statement>
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<p>3</p>
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</statement>
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<feedback>
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<p>This would be true if it was returning the item at index 1 or -3.</p>
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</feedback>
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</choice>
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<choice correct="yes">
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<statement>
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<p>buy</p>
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</statement>
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<feedback>
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<p>This is returning the second to the last item, the one at index -2.</p>
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</feedback>
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</choice>
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<choice>
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<statement>
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<p>4</p>
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</statement>
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<feedback>
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<p>This would be true if it was returning the item at index 3 or -1.</p>
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</feedback>
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</choice>
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<choice>
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<statement>
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<p>Nothing, there will be an error.</p>
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</statement>
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<feedback>
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<p>This code will run without any errors.</p>
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</feedback>
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</choice>
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</choices>
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</exercise>
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</subsection>
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<subsection xml:id="flal_built-in-functions-that-work-on-lists">
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<title>Built-in Functions That Work on Lists</title>
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<p>There are several built-in functions in Python that work on lists such as <c>max</c>, <c>min</c>, <c>len</c>, and <c>sum</c>.</p>
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<exercise label="flal_ll_ac_list_func">
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<statement>
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<p>Run this code to see what it prints. You can also step through the code using the "Show Codelens" button. </p>
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</statement>
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<program xml:id="flal_ll_ac_list_func_editor" interactive="activecode" language="python">
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<input>
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# function definition
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def list_func(my_list):
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print("max", max(my_list))
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print("min", min(my_list))
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print("len", len(my_list))
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print("sum", sum(my_list))
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# function definition
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def main():
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list_func([1, 2, 3])
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list_func([90, 100])
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# function call
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main()
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</input>
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</program>
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</exercise>
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<exercise label="flal_avg_drop_high_and_low">
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<statement>
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<p>Write a function <c>avg_with_drop</c> that takes a list, <c>num_list</c> and returns the average of the values in the list, but it does not include the highest or lowest value in the average. For example, <c>avg_with_drop([1,2,3,4])</c> should return <c>2.5</c>.</p>
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</statement>
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<program xml:id="flal_avg_drop_high_and_low_editor" interactive="activecode" language="python">
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<input>
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def avg_with_drop(num_list):
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====
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from unittest.gui import TestCaseGui
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class myTests(TestCaseGui):
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def testOne(self):
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self.assertEqual(avg_with_drop([1,2,3,4]), 2.5, 'avg_with_drop([1,2,3,4])')
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self.assertEqual(avg_with_drop([2,4,6,8]), 5, 'avg_with_drop([2,4,6,8])')
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self.assertEqual(avg_with_drop([10, 80, 100, 60]), 70, 'avg_with_drop([10, 80, 100, 60])')
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self.assertEqual(avg_with_drop([-10, 80, 120, 60]), 70, 'avg_with_drop([-10, 80, 120, 60])')
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self.assertEqual(avg_with_drop([5, 10, 15, 20]), 12.5, 'avg_with_drop([5, 10, 15, 20])')
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myTests().main()
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</input>
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</program>
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</exercise>
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</subsection>
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<subsection xml:id="flal_list-methods">
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<title>List Methods</title>
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<p>Lists are objects of the <c>list</c> class and have methods that operate on list objects using dot notation (<c>name.method()</c>) such as <c>append</c>, <c>pop</c>, and <c>extend</c>.</p>
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<exercise label="flal_ll_ac_list_methods">
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<statement>
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<p>Run this code to see what it prints. You can also step through the code using the "Show Codelens" button.</p>
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</statement>
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<program xml:id="flal_ll_ac_list_methods_editor" interactive="activecode" language="python">
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<input>
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# function definition
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def list_methods(alist):
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print(type(alist))
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print(alist)
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alist.append(3)
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print(alist)
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alist.append([2])
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print(alist)
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alist.pop(1)
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print(alist)
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alist.extend([8, 11])
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print(alist)
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# function definition
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def main():
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l1 = [1]
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list_methods(l1)
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print(l1)
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l1 = ['hi', 'bye']
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list_methods(l1)
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print(l1)
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# function call
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main()
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</input>
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</program>
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</exercise>
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<exercise label="flal_list_append_pop_predict">
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<statement>
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<p>What would the following code print?</p>
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<program language="python">
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<input>
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def list_trans(lst):
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lst.append(3)
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lst.pop(2)
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return lst
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l1 = [2, 5, 7]
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print(list_trans(l1))
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</input>
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</program>
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</statement>
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<choices>
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<choice>
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<statement>
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<p>[2, 5, 7, 3]</p>
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</statement>
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<feedback>
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<p>This is what the list looks like before the pop executes.</p>
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</feedback>
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</choice>
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<choice>
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<statement>
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<p>[5, 7, 3]</p>
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</statement>
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<feedback>
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<p>This would be true if pop removed the first value that was passed in, but it takes an index and removes the item at that index.</p>
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</feedback>
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</choice>
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<choice>
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<statement>
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<p>[2, 7, 3]</p>
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</statement>
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<feedback>
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<p>This would be true if pop removed the item at index 1, but it removes the item at index 2 and the first item is at index 0.</p>
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</feedback>
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</choice>
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<choice>
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<statement>
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<p>[2, 5, 7]</p>
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</statement>
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<feedback>
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<p>This would be true if pop removed the last item, but it removes the one at index 2.</p>
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</feedback>
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</choice>
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<choice correct="yes">
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<statement>
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<p>[2, 5, 3]</p>
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</statement>
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<feedback>
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<p>Correct. This adds 3 at the end and then removes the item at index 2.</p>
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</feedback>
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</choice>
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</choices>
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</exercise>
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<note>
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<p>Lists are mutable (changeable). List methods like <c>append</c> and <c>pop</c> change the current list.</p>
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</note>
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<p>You can also reverse a list or sort it.</p>
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<exercise label="flal_ll_ac_list_methods2">
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<statement>
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<p>Run this code to see what it prints.</p>
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</statement>
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<program xml:id="flal_ll_ac_list_methods2_editor" interactive="activecode" language="python">
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<input>
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# function definition
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def list_methods2(alist):
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print(alist)
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alist.reverse()
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print(alist)
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alist.sort()
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print(alist)
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alist.sort(reverse = True)
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print(alist)
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# function definition
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def main():
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l1 = [-2, 50, -20, 30]
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list_methods2(l1)
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print(l1)
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l1 = ['hi', 'bye', 'apple']
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list_methods2(l1)
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print(l1)
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# function call
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main()
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</input>
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</program>
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</exercise>
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<exercise label="flal_list_result_of_reverse">
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<statement>
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<p>What is the last thing the following code prints?</p>
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<program language="python">
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<input>
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def list_trans(lst):
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r = lst.reverse()
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print(lst)
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print(r)
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l1 = [2, 5, 7]
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list_trans(l1)
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</input>
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</program>
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</statement>
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<choices>
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<choice correct="yes">
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<statement>
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<p>None</p>
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</statement>
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<feedback>
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<p>It prints the return value from the reverse method which is None.</p>
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</feedback>
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</choice>
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<choice>
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<statement>
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<p>[2, 5, 7]</p>
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</statement>
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<feedback>
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<p>This would be true if it printed the value of</p>
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</feedback>
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</choice>
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<choice>
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<statement>
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<p>[7, 5, 2]]</p>
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</statement>
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<feedback>
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<p>This would be true if pop removed the item at index 1, but it removes the item at index 2 and the first item is at index 0.</p>
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</feedback>
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</choice>
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<choice>
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<statement>
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<p>Nothing, there will be an error.</p>
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</statement>
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<feedback>
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<p>This would be true if pop removed the last item, but it removes the one at index 2.</p>
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</feedback>
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</choice>
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</choices>
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</exercise>
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</subsection>
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<subsection xml:id="flal_the-for-each-loop">
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<title>The For-Each Loop</title>
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<p>A for-each loop in Python will loop though the items in a list starting with the item at index 0, then index 1, and so on till the last item in the list.</p>

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