CS111 – Fundamentals of CS�Lecture 13�Python IV�

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Mohammad El-Ramly, PhD

Fall 2021-2022

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http://www.acadox.com/class/63592 6EQYX4

https://www.geeksforgeeks.org/python-programming-language/

Reading for this & last lectures

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1. Python Crash Course (Chapters 1 to 8 and 10)
2. Share any useful resources you find
3. https://www.freecodecamp.org/
4. https://www.w3schools.com/python/default.asp

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Lecture 10 Outline

1. Merge Sort
2. Ternary Operator
3. Tuples
4. More on Lists

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Remember

• Any fool can write code that a computer can understand. Good programmers write code that humans can understand. 
• Martin Fowler, 2008.

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1. Merge Sort

Base Case

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Divide

Conquer

1. Merge Sort

def merge_sort (lst):

length = len(lst)

if length == 1:

return lst

else:

half1 = lst[:length//2]

half2 = lst[length//2:]

return (merge (merge_sort(half1),\

merge_sort(half2)))

1. Merge Function

def merge(lst1, lst2):

i, j = 0, 0

result = []

while i < len(lst1) and j < len(lst2):

next = lst1[i] if lst1[i] < \

lst2[j] else lst2[j]

result.append(next)

(i,j) = (i + 1, j) if lst1[i] < \

lst2[j] else (i, j + 1)

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result.extend(lst1[i:])

result.extend(lst2[j:])

return result

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2. Ternary Operator

next = lst1[i] \

if lst1[i] < lst2[j] \

else lst2[j]

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if lst1[i] < lst2[j]:

next = lst1[i]

else:

next = lst2[j]

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2. Ternary Operator

valu1 if condition else value2

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• var = x if x < y else y
• var = "even" if x % 2 == 0 \

else "odd"

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3. Tuples

• See Slides
• Tuples are more memory efficient than the lists. When it comes to the time efficiency, again tuples have a slight advantage over the lists especially when lookup to a value is considered. If you have data which is not meant to be changed in the first place, you should choose tuple data type over lists
• https://www.programiz.com/python-programming/list-vs-tuples

3. Tuples

• lst = [3,4]
• tup = (3,4)
• lst.__sizeof__() # 56 tup.__sizeof__() # 40

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4. Lists

• lst = [1, 2] * 3
• lst = [1, 2] + [3, 4]
• lst += [5, 6]
• lst.extend ([7, 8])
• lst.append (9)
• lst.insert (0, -100)
• lst.insert (-1, 300)
• dir (lst)

4. List Functions

• lst.pop (index)
• lst.remove (item)
• lst2 = lst.copy()
• lst.sort()
• lst.reverse()
• lst.clear()

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